The invention provides a key, a key module and a key device. The key comprises a key main body, connecting points convexly arranged on the key main body and a resistor located in the key main body and connected with the connecting points. The key module comprises module main bodies each provided with a containing groove and signal leads; each containing groove matches each key main body; conductive contacts are arranged in each containing groove; the signal leads are connected with the conductive contacts; and when keys are inserted into containing grooves and are pressed down, the connecting points of the keys are in contact with the conductive contacts to enable the signal leads to be electrically connected with the resistor of the key. The key device comprises at least one key module, the keys located in the containing grooves of the key modules, and a processing circuit connected with the signal leads of the key modules and used for detecting the signal leads and executing functions corresponding to the keys if the signal leads are detected to be electrically connected to the resistors of a plurality of keys. By adoption of the scheme, users can assemble wanted key devices based on personalized needs.