The feasibility of measuring object’s phase using coherent light illuminated schlieren (CLIS) apparatus is investigat ed by numerical simulations.Simulation results show that when the knife edge of the schlieren apparatus is placed horizontally and a square object with uniform phase or nn-uniform phase only varied along the horizontal direction is imaged, at the image plane the light intensity difference between the upper and lower ar eas outside the object is proportional to the sine of the object’s phase.Furthe rmore,for a square object with non-uniform phase varied only along the directio n perpendicular to the knife edge,the intensity difference actually presents the sine of the area-weighted average phase of the object if only the phase variat ion is limited in the range of [kπ/2,(k+1) π/2] (k is an integer).Similar conclusions are also found for objects with other shapes.By CLIS the sine of an object’s p hase can be obtained,and the phase value in the range of [kπ/2,(k+1)π/2] (k is an in teger) is thus determined.In addition,the effects of the knife edge’s position, the size and transmittance of the under-test object are also discussed.It sugge sts that CLIS can determine the sine of an object’s phase and provide semi-qua ntitative phase measurement when the object’s phase has not much spatial variat ion.