Basal body temperature reflects a woman’s ovarian function. A drop in basal body temperature after the eleventh day of ovulation indicates that the luteal phase is coming to an end and the menstrual phase is approaching. After the onset of menstruation, i.e. the follicular phase, the basal body temperature is usually on the low side; after ovulation, i.e. the luteal phase, the body temperature will rise again, with an increase of about 0.3°C. The body temperature will rise again after ovulation, i.e. the luteal phase. This cycle proceeds in such a way that the body temperature keeps changing with the menstrual cycle. When the luteal phase ends immediately after eleven days of ovulation, the menstrual phase is approaching, so there is a drop in body temperature. Therefore, women can measure their basal body temperature to pay attention to their menstrual cycle change rules as well as ovarian function, if there is a basal body temperature in the ovulation period after the decline of too fast and other situations, it is recommended to go to the hospital to seek medical treatment, regulate their endocrine level.