Fertilized egg usually lies in bed in 6~7 days and not later than 10 days. After the sperm and egg meet, the fertilized egg will be formed in about 30 hours. The fertilized egg will move towards the uterine cavity with the help of peristaltic movement of the fallopian tube and the push of the epithelial cilia of the fallopian tube, and it will start to show oogenesis and form several daughter cells while moving. There are some necessary conditions for the fertilization of the egg, the need for the body to secrete a sufficient amount of estrogen and progesterone, and the endometrium of the tolerance only in the menstrual cycle between 20 to 24 days to have, also called the window period, only in the window period to allow the fertilization of the egg to bed, so the fertilization of the egg is generally in the 6 ~ 7 days to bed, the latest will not exceed 10 days. Each person’s physical condition is different, the time of implantation may be different, can not be generalized, if the body has abnormalities, should be timely consultation.