I. Standard hospitalization process of the clinical pathway for children with APL in complete remission (i) The standard hospitalization days are within 28 days. (B) Entry pathway criteria. 1. The first diagnosis must be in accordance with the Acute Promyelocytic Leukemia (APL) disease code for children (ICD-10: C92.402, M9866/3). 2, Complete remission (CR) achieved with induction chemotherapy. 3.Patients can enter the pathway when they also have other disease diagnoses but do not require special treatment during hospitalization and do not affect the implementation of the clinical pathway process for the first diagnosis. (C) It takes 2 days (meaning working days) to perfect the routine examination for admission. 1.Required examination items: (1) routine blood, routine urine, routine stool; (2) liver and kidney function, electrolytes, coagulation function, blood type, pre-transfusion examination; (3) chest X-ray plain film, electrocardiogram, abdominal ultrasound. 2, Fever or suspected infection of a system can be selected: pathogenic microbial culture, imaging examination. (3) Bone marrow smear examination or/and biopsy (if necessary), micro residual lesion detection. 4.Patients and family members sign the following consent forms: informed consent for chemotherapy, consent for bone puncture, consent for lumbar puncture and intrathecal injection, informed consent for blood transfusion, informed consent for intravenous cannulation. (iv) Chemotherapy was started within the 3rd day of admission. (V) Chemotherapy regimen. 1. Post-remission consolidation therapy: 3 courses of chemotherapy are feasible, and the available regimens are DA, MA, HA regimen or DNR, MTZ or ATO combined with ATRA alone: (1) DA regimen: DNR 40-45mg・m-2・d-1×3d, Ara-C 100-200mg・m-2・d-1×7d. (2) MA regimen: MTZ 6- 10mg・m-2 ・d-1×3d, Ara-C 100-200mg・m-2・d-1×7d. (3)HA protocol: HHT 2.0-4.0mg・m-2 ・d-1×7-9d, Ara-C 100-200mg・m-2・d-1×5-7d. (4)DNR alone: DNR 40-45mg・m-2・d- 1×3d. (5) MTZ alone: MTZ 6-10mg・m-2 ・d-1×3d. (6) ATRA+ATO: ATRA 20-30mg・m-2・d-1×28d, ATO 0.2mg・Kg-1・d-1×28d. In case of high-risk patients (WBC ≥10×109/L at initial diagnosis), the DA or MA regimen can be changed from Ara-C for 1-2g・m-2, q12h ×3d. 2. Prevention and treatment of central nervous leukemia (CNSL): lumbar puncture and intrathecal injection at least 4 times, confirmed CNSL withdrawal from this pathway. The intrathecal injection regimen is as follows: MTX: age <12 months 6mg, age 12-36 months 9mg, age >36 months 12.5mg; Ara-C: age <12 months 15mg, age 12-36 months 25mg, age >36 months 35mg; DXM: age <12 months 2.5mg, age 12-36 months 2.5mg, age >36 months 5mg. 3, Maintenance therapy after remission, sequential application of ATO, ATRA, 6-MP+MTX or 6-TG+Ara-C regimen for 5 cycles. (1) ATO 0.2mg・Kg-1 ・d-1×14-28d. (2) ATRA 20-30mg・m-2 ・d-1×14-28d. (3) 6-MP+MTX or 6-TG+Ara-C: ①6-MP+MTX: 6-MP 50-100mg・m-2・d-1 for 12 weeks orally, MTX 20mg・m- 2, once a week for 12 weeks. ②6-TG+Ara-C: 6-TG 75 mg・m-2 ・d-1×7d, Ara-C 100 mg・m-2・d-1×7d. (F) Examination items for review during the recovery period after chemotherapy. 1.Blood routine, liver and kidney function, electrolytes. 2.Organ function assessment. 3.Bone marrow examination (if necessary). 4.Micro residual lesion detection (if necessary). (VII) Treatment during and after chemotherapy. 1.Infection prevention and control: patients with fever are recommended to have immediate pathogenic microbial culture and use antibacterial drugs, cephalosporins (or penicillins) can be used for anti-inflammatory treatment; those whose fever does not resolve after 3 days can be considered to replace carbapenems and/or glycopeptides and/or antifungal treatment; patients with definite organ infection should choose corresponding antibacterial drugs according to the infection site and pathogenic microbial culture results. 2.Prevent and control organ function damage: antiemetic, hepatoprotective, hydration, alkalinization. 3.Component transfusion: for patients with Hb80g/L, PLT20×109/L or active bleeding, transfuse concentrated red blood cells, single or multi-collection platelets, respectively. The indications for transfusion can be relaxed for those with cardiac insufficiency. 4. Hematopoietic growth factor: Absolute neutrophil value (ANC) ≤ 1.0×109/L after chemotherapy, G-CSF 5μg・Kg-1 ・d-1 can be used. (H) Discharge criteria. 1.Generally good condition. 2. No complications and/or comorbidities requiring inpatient management. (ix) Variation and cause analysis. 1, Those with infection, anemia, bleeding and other comorbidities during or after treatment for related diagnosis and treatment may prolong hospitalization and result in increased costs. 2.If the cerebrospinal fluid examination after lumbar puncture shows the presence of CNSL, withdraw from this pathway and enter the related pathway. 3.If relapse occurs during the treatment, withdraw from the pathway.