Aiming at the nonuniformity of object surface coating, laser is adopted in contactless measurement of object surface. By this way, online detection of microcosmic variations in the object surface is realized. Through scanning over the object surface with a light spot and analyzing the variation of intensity of reflected light, the relationship between reflected light intensity and object surface coating uniformity can be obtained. Uniformity of object surface coating is radom, and the reflectivity is different on the surface. The appearance features of object surface to be measured are emulated by computer, and the simulated results can reflect the change tendency of surface coationg uniformity. Experimental results prove that the measurement system has simple structure and intuitionisticprinciple, and precision of measurement value is less than 5 μm within an operation scope from 1～80 μm.