The invention provides a diaphragm and a preparation method thereof, and an MEMS microphone. The diaphragm includes a intermediate vibration part and a fixed part surrounding the vibration part. The vibration part includes multiple vibration sub-parts, which are distributed stepwise along the vibration direction of the diaphragm. Multiple vibration sub-parts are distributed stepwise along the vibration direction of diaphragm. The effective area of the diaphragm is increased, and the stress can be adjusted by the height of the ladder and its inclination angle. The mechanical sensitivity of the MEMS microphone containing this diaphragm is improved, resulting in a high-performance, small-sized MEMS microphone.