A fastening device and fastening method for fastening a distribution box control panel to a distribution box, the fastening device comprising a push block, a biasing member, a shell, and a locking member sleeved in the shell, wherein the method utilizes the biasing force of the biasing member to fasten the device, and utilizes the elasticity of the locking member having a bending structure to realize assembly and disassembly, where a user can conveniently assemble the device with hand alone, i.e., during assembly, the fastening device is pushed in along a notch in the distribution box control panel and then pressed tightly, and during disassembly, the fastening device can be pushed out after the locking member is pressed such that in comparison to a screw fastening method, the fastening device of the present invention provides a constant fastening force, thus realizing more stable and reliable fastening.