There are many interference fringes and speckle on the screen of laser projection display system during to the strong coherent characteristic of laser. In order to eliminate the influence of interference fringes and speckle on image quality, temporally averaged patterns was obtained by rotating a new kind of diffuser called Engineered DiffuserTM. First, the reason of speckle formation and the theory of speckle suppression through temporally averaged patterns were introduced. Then the differences on structure and function between traditional diffuser ground glass and Engineered DiffuserTM were analyzed. Finally, the speckle suppresion experiment by rotating Engineered Diffuser in laser projection display system was established. The effect of speckle suppresion was tested by comparing other speckle suppression methods. Experimental results indicate that the speckle contrast is weakened to 3.08%. The patterns quality is good and has no interference fringes. It can satisfy the laser projection display system requirements of small volume, simple practice and so on.