Expander-assisted two-stage breast reconstruction consists of two steps: (1) implantation of the expander after breast cancer surgery, with regular postoperative dilatation by water injection, which takes 3-5 months; (2) a second-stage surgery when the predetermined dilatation capacity has been reached, with removal of the expander and implantation of the prosthesis. If the nipple areola has been removed, nipple areola reconstruction surgery is also required. Stage II breast reconstruction surgery is indicated in cases of breast cancer where more skin has been removed during surgery, the breast flap has poor blood flow, and the breast is large in size. The slow expansion process allows the breast flap to gradually expand, improve blood flow and eventually reach a larger breast volume, avoiding complications such as necrosis and incision splitting due to poor blood flow and high tension in the flap caused by the implantation of prosthesis in the first stage. There are two types of expanders. One is a specialized expander with a magnetic directional device, built into the injection pot, such as the Mentor-CPX-4 expander. The other is an ordinary disk-shaped dilator without a magnetic directional device, and the injection pot can be placed either externally or internally, with the majority of cases being placed externally. In cases where the injection jug is external, care should be taken to care for the catheter inlet during the injection and dilatation process to prevent retrograde infection. Patients can live and work normally during the interval between procedures.