A small liquid crystal display that acted like a grating and phase-shifting device was used on Ronchi test,to measure a spheric or an aspheric of large wavefront aberration,more quickly and accurately.Instead of a common grating and a step motor,a movable image of grating is shown on the liquid crystal display. This gets rid of the phase-shifting error caused by the motor moving,and the error caused by grating revolve angle not being just 90°. A phase-shifting algorithm is used to test an aspheric,and the wavefront aberration of the aspheric is restored. The experiment shows that a small liquid crystal display can be used a grating and phase-shifting device.