The action principle of IUD is mainly manifested in the following four aspects: 1. Mechanical action: as a foreign body, it causes mild, chronic and non-bacterial inflammatory reaction of endometrium, thus changing the intrauterine environment and preventing pregnant eggs from implantation. Second, the role of inflammatory cells: after the denatured substances of inflammatory cells reach a certain concentration, they poison the embryo and make it unable to continue to develop. 3. Phagocytosis: Macrophages and neutrophils mainly play the role of phagocytosis and destruction of sperm. 4. Function of active substances: IUD can be made of copper, which can achieve the purpose of contraception through the local changes of internal environment such as endometrium and uterine cavity fluid and its toxic effect on sperm. V. Role of Prostaglandin: IUD can stimulate the endometrium to produce prostaglandin, which makes the contraction and peristalsis of uterus and fallopian tubes abnormal, and at the same time enhances the role of estrogen, which makes the intrauterine environment not conducive to implantation. The above are some principles of IUD. Experts remind that it is very important to take necessary contraceptive measures to maintain health, so everyone must actively take various preventive measures to avoid accidents. Let the body suffer more damage.