Expander injection is a method of gradually making the expander fill larger by expanding the water injection, while driving the surface skin to gradually expand. Preoperative shower is required to wash off the dirt and reduce the number of bacteria in the scarred area, and shave off the hair in and around the area, such as armpit hair, beard and hair. Take care that the skin in the area is intact and free of boils. Avoid eating blood-activating diets such as hot pot before surgery. Generally, the first watering must be carried out within 2 weeks after the operation, and the watering and the removal of stitches should not be carried out on the same day, it is better to be separated by more than two days. Generally 1-3 times per week, and keep a record. Failure to perform the first water shot for more than two weeks may result in the formation of a peritoneal capsule and the dilator not being able to hit, thus causing ineffective surgical dilatation. The first three water injections can be done as much as possible without pain to the skin so that the dilator can be held up in a rounded manner to prevent the dilator from folding into an angle and injuring the skin. After the dilatation injections are complete, they need to be stopped and maintained for 3-4 weeks to help minimize skin retraction, large skin output, flap stabilization, reduced chance of flap necrosis, reduced incisional tension, and a narrower incision, which helps to reduce scarring.