A height adjusting mechanism for an inlet valve includes a valve body, and inlet pipe, a retaining member and an actuator. The inlet pipe is sleeved in the valve body and connected to the valve body; the retaining member is assembled in the valve body; and the actuator can drive the retaining member to move to make the valve body fixed to the inlet pipe or moved relatively to the inlet pipe in the axial direction. The actuator drives the retaining member to move in order to let the valve body and the inlet pipe to be fixed or moved relatively to each other in the axial direction. There is no need to rotate the valve body during adjusting process, and the float won't affect the tank wall when the water valve body is rotating.