The reason of the two kinds of optical noise including grid noise and speckle noise is analyzed. A method of reducing the both two kinds of optical noise by a moving random phase plate is introduced. And the theoretic principle is deduced. A micro projector model is designed, in which a random phase plate is driving for vibration by a micro electric controlled motor. The projected imaging was obtained by a CCD camera with different F# and exposure time. The speckle contrast of the projected imaging is calculated. It is shown in the results that when the random phase plate is static, the grid noise can be reduced well. When the random phase plate is vibrated in a frequency higher than the frequency based on the vision hysteresis, the two kinds of optical noise can both be reduced. The final speckle contrast of the projected imaging is less than 5%, which can be satisfied with the projection display application.