Based on the idea that the cat-eye effect reflected light of defocused optical lens can be regarded as a spherical wave, and by using Collins formula and the method of expanding the aperture function into a finite sum of complex Gaussian functions, the distribution formula of the cat-eye effect reflected light interfered with the reference incident light is deduced. Through numerical computation, laws governing the variation of the distribution and stripe series of the interference field with the focal shift are obtained. Then an experiment is done to validate the laws. The results show that off-focus of the optical lens is a necessary condition for the cat-eye effect reflected light to be interfered with the incident light and stripes are brought, the interference cirque gradually moves inside and the stripe number becomes larger with the increasing of the focal shift, and the relation between the interference stripe number and the focal shift can be correctly described by the geometric optical path function on nearby condition.