Abstract: Aiming at the problems encountered in the actual inspection work and the requirements proposed in the GB/T 108992009 for test method of stray light in an optical system, we discussed the necessity for testing the stray light coefficient in the full field of an optical system and the corresponding methods of measurement. Through the transformation of the existing stray light testing device, we achieved the testing of stray light coefficient in the full field of an optical system, and gave the test results and distribution curves of stray light coefficient in the full field of 2 kinds of zoom lenses. It is concluded that there is a great difference in stray light coefficient and distribution between the lenses which have similar parameters but different models,and the different form of optical and mechanical structure is the main reason for this difference.The measurement data can offer a reference for improving the suppression ability of stray light in optic systems.