A MEMS microphone, a microphone unit and an electronic device are disclosed by the present disclosure. The micro-electro-mechanical system microphone comprises: a substrate; a back electrode plate comprising a supporting structure; and a diaphragm located between the substrate and the back electrode plate, wherein the supporting structure comprises a supporting portion used for supporting a periphery of a diaphragm, and a supporting electrode being insulated from the supported diaphragm, and wherein the diaphragm is a stress-free film when being applied no bias, and when being applied a bias, the supporting electrode constrains the periphery of the diaphragm on the supporting portion through electrostatic interaction so as to support the diaphragm in a clamped manner.