A diaphragm for a micro loudspeaker includes an outer casing that is provided with a through-hole, a membrane that is disposed in the through-hole, and a suspension that connects the membrane and the outer casing. The outer casing is provided with an inner wall that wraps into the through-hole. The suspension includes an effective operation zone that is extended from the inner wall into the through-hole, and a fixed area that is extended from the inner wall to outside the through-hole. The fixed area of the suspension is provided with a cut-off area, which keeps the effective operation zone at a good intactness, and enables the membrane to vibrate up and down more uniformly, thereby improving the sound quality of micro loudspeaker.