Safety period contraception, also known as natural contraception, is based on a woman’s menstrual cycle to project the ovulation date, in determining the date of the menstrual cycle that is easy to conceive, to avoid intercourse and achieve the purpose of contraception, including the calendar method, temperature monitoring method, cervical mucus observation method. 1, the calendar method is mainly applicable to women with regular menstrual cycle, ovulation usually occurs 14 days before the next menstrual flow, according to this projection 4-5 days before and after ovulation as the 2. Basal body temperature and cervical mucus observation method, which is based on the change of basal body temperature and cervical mucus to determine the ovulation day, the change of basal body temperature curve and ovulation is not constant; cervical mucus observation, after training to master. These two methods, in general, are not very accurate, so it is not recommended to use safe period contraception.