The safe period is calculated according to the menstrual period. Safe period is based on menstruation to calculate the time, if a woman’s menstruation is more regular, about 28 days to a menstruation, about 14 days before the next menstruation ovulation, couples after coitus, sperm can survive in the woman’s vagina for 2 to 3 days, the egg from the ovaries can survive for 1 to 2 days, so the 3 days before the day of ovulation and the 3 days after the day of ovulation belong to the dangerous period. The period from clean menstruation to 3 days before ovulation belongs to the pre-ovulation safe period, and the period from the 3rd day after the day of ovulation to 1 day before the next menstrual period belongs to the post-ovulation safe period. Safe period contraceptive method is only suitable for women who ovulate and menstruation is relatively regular, if the menstruation is usually irregular, often early or delayed, and the time of ovulation is not fixed, can not be in accordance with this method of contraception, it is very likely to have an unwanted pregnancy, it is recommended that other contraceptive measures, such as intrauterine device, condoms and so on. Women are advised to adopt contraceptive measures suitable for themselves to minimize unwanted pregnancies.