A battery pack, an assembly method for battery pack, and a disassembly method for battery pack are provided. The battery pack includes a battery box and a battery. The battery is provided in the battery box. The battery box includes a main frame, and the main frame includes a first portion and a second portion. The first portion and the second portion are stacked up, and the first portion and the second portion are detachably connected to each other. The battery is connected to the first portion, or the battery is connected to the second portion.