Stray light is one of the important factors affecting the image quality of microscopy systems. During the processing of optical elements, stray light caused by specular scattering can not be ignored. Taking microscope objectives with 20× magnification and NA=0.49 as a typical example and using the optical analysis software TracePro, a simulation model of measuring veiling glare of microscope objectives is built up. Through analyzing the factors affecting the model with different illuminance numerical apertures, different illuminance fields and different black spot positions, the feasibility of the model is verified. On this basis, the stray light intensity on the image plane with different NA microscope objectives is simulated quantitatively under the condition of different surface roughness (2, 5, 10, 20 nm) and different cleanliness levels (250, 500, 750). The results indicate that the surface roughness greater than 10 nm and the cleanliness level higher than 500 will change the stray light intensity distribution on the image plane, and affect the system performance significantly, especially for those microscope objectives with large NA. It is of critical importance to keep the surface of optical elements clean and to improve the processing technology of optical elements.