HCG is human chorionic gonadotropin, ectopic pregnancy HCG drop after rebound reasons are residual active chorionic villi, re-pregnancy, trophoblastic tumors and so on. 1. Residual active chorionic villi: after ectopic pregnancy drug treatment, trophoblast cells are not completely killed, and some active trophoblast cells secrete human chorionic gonadotropin again; conservative surgery for ectopic pregnancy, such as the umbrella of the fallopian tube pregnancy extrusion of the pregnancy, the trophoblast cells are not completely eliminated, and the residual trophoblast cells secrete human chorionic gonadotropin again, which results in the occurrence of this phenomenon. 2. Re-pregnancy: after ectopic pregnancy surgery, patients have intercourse during the ovulation period, resulting in another pregnancy, the fertilized egg trophoblast cells secrete chorionic gonadotropin, resulting in ectopic pregnancy chorionic gonadotropin levels drop to normal and then rebound again. 3. Trophoblastic tumors: a few trophoblastic tumors can be secondary to ectopic pregnancy, the tumor cells are composed of trophoblastic cells, which can secrete human chorionic gonadotropin, causing ectopic pregnancy human chorionic gonadotropin to drop and then rebound. Ectopic pregnancy human chorionic gonadotropin level drop after rebound need to consult the doctor in time, under the guidance of the doctor to identify the cause of the disease, give further treatment.