The present invention provides a method for manufacturing a thermal bimorph diaphragm and a MEMS speaker with thermal bimorphs, wherein the method comprises the steps of: thermally oxidizing a substrate to obtain an insulating layer thereon and providing a metal layer on the insulating layer; providing a sacrificial layer on the metal layer; providing a first thermal bimorph layer on the sacrificial layer; providing a second thermal bimorph layer on the first thermal bimorph layer; providing a metal connecting layer at the positions on the metal layer where the sacrificial layer is not provided; forming corresponding back holes on the substrate and the insulating layer and releasing the sacrificial layer; forming the thermal bimorph diaphragm which is warped with the first thermal bimorph layer and the second thermal bimorph layer after the sacrificial layer is released.