The depth of sternum subsidence during CPR is 5-6 cm. Chest heart compression during CPR is to produce blood flow by regular and forceful compression of the sternum to a certain depth. In order to achieve the purpose of compression, it is required that there must be a certain depth of compression, both to ensure the effect of compression and to minimize the complications of compression. Through repeated studies, scholars finally believe that the compression depth of 5-6cm is the most appropriate, neither less than 5cm nor more than 6cm, more than 6cm compression depth may fracture the sternum and ribs, resulting in cardiopulmonary injuries and other compression complications. If the depth of compression is less than 5cm, although there are fewer compression complications, there is no good compression effect achieved with a compression depth of more than 5cm.