Medication abortion is a common abortion method, but at present, medication abortion is not always successful in clinical practice. There are many reasons for the failure of medication abortion, which are roughly divided into the following points. First, the embryo is too active. Medication abortion starts with the oral administration of mifepristone. Mifepristone can reduce or even kill the embryonic activity and facilitate the discharge of the body. However, if the embryo is too active, then mifepristone will not be able to kill the embryo, which will result in the embryo not being easily expelled in the endometrium. Second, abortion. If a pregnant woman has a history of previous abortion, then abortion can cause artificial damage to the uterine cavity. If the current gestational sac lays in the injury, adhesions between the gestational sac and the endometrial muscle layer may occur, making it difficult to expel. If the pregnancy at the scar occurs, then the abortion will not only fail but also cause abdominal pain and heavy vaginal bleeding, which may endanger the patient’s life in serious cases. Thirdly, the embryo has stopped developing for too long. If the dead embryo stays in the uterus for too long, the greater the possibility of adhesions, and the higher the failure rate of medical abortion at this time. In summary, the reasons for failure of medication abortion include: strong embryonic activity, history of abortion and prolonged embryonic arrest.