The present disclosure provides a protection casing assembly for a wearable device. The protection casing assembly includes a main case and a frame. The main case has a first accommodation space and configured to allow a wearable device to be disposed detachably. When the wearable device is disposed in the first accommodation space, the wearable device and the main case define a second accommodation space adjacent to at a device surface of the wearable device. The frame is detachably disposed in the second accommodation space.