1. Hydration and alkalinization: (1) The total fluid volume of d0 is 1500 ml/m2, and the total daily fluid volume of d1-3 is 3000 ml/m2. d0 hydration is started 12 hours before MTX and maintained until d1 before MTX chemotherapy. (2) For d0-3 hydration, 5% sodium bicarbonate is one-tenth of the total fluid volume. (3) If there are still other chemotherapeutic drugs in d1-3, which occupy part of the fluid volume, this part of the fluid volume must be deducted, i.e., to ensure that the total daily fluid volume is 3000 ml/m2. (4) In pediatric patients with imperfect renal sodium excretion function, except for sodium bicarbonate, 5% glucose is used for all other fluids. (5) The fluid used for hydration and alkalinization must be continuously infused for 24 hours, do not stop within a few hours after the drip. 2.MTX dosage: According to the condition, calculate the total amount of MTX according to the body table. 3.MTX usage: One tenth of the total amount of MTX should be finished within 30 minutes, and the remaining nine-tenths should be finished within 23.5 hours. The exceptions are osteosarcoma (MTX drip for 6 hours) or low-risk lymphoma (MTX drip for 4 hours), where the total amount of MTX can be dripped within the specified time without first dripping one-tenth within 30 minutes. 4. CF relief: The dose is 15 mg/m2, started 12 hours after the end of MTX, q6h×7 times (for those who have been on MTX for 24 hours) or q6h×10 times (for those who have been on MTX for 6 hours), i.e. the last CF is used at the 72nd hour after the start of MTX. It can be increased or decreased appropriately according to the MTX blood concentration. 5. Monitoring items: (1) Record 24-hour urine volume, d0-3 (2) Urine routine, d1-3 (3) Measure urine PH value, d0-3, and notify the doctor when urine PH value is <7 or >9 (4) Measure MTX blood concentration at MTX 0, 24, 48, 54, 72 hours. Osteosarcoma (MTX titrate 6 hours) or low risk lymphoma (MTX titrate 4 hours) must increase the time point of 6 hours or 4 hours. 6. Precautions: (1) MTX must be administered only after normal blood picture and liver and kidney function. MTX is contraindicated in patients with body fluid such as pleural, pericardial and abdominal cavities to avoid increased toxicity. (2) Ask the patient daily about urine volume, urine PH value, and whether there are any precursors of MTX toxicity, such as rash, oral mucosal ulcer, abdominal pain, diarrhea, etc. If there is any abnormality, find the cause and deal with it in time. (3) If a decrease in urine volume is found, the urine PH value, MTX blood concentration, urinary routine, renal function, etc. should be investigated, and tachypnea should be given to diuretic. (4) If the urine PH value is <7 at any time, increase sodium bicarbonate immediately (either orally or intravenously); if the urine PH value is >9, reduce alkaline supplementation appropriately. (5) If MTX is not finished within the specified time, regardless of the cause, it must be discarded and the drip time must not be extended, otherwise the toxicity will increase. (6) Timely tracking of MTX blood concentration results, 48 hours of results is particularly important. If the MTX blood concentration at 48 hours is outside the safe range, additional CF dosage should be administered as follows until the next MTX blood concentration result is within the safe range: if the MTX concentration is 1×10-6mol/L, then CF should be 30mg/m2; if the MTX concentration is 2×10-6mol/L, then CF should be 45mg/m2; if the MTX concentration is 3×10-6mol/L, then CF should be 45mg/m2. If the MTX concentration is 3×10-6mol/L, then CF is 60mg/m2 ……; if the MTX concentration is >5×10-6mol/L (assume n×10-6mol/L), then CF dosage is “patient’s body weight (Kg) × n”. At the same time, additional hydration and alkalinization until the MTX blood concentration is normal.