Based on the generalized Collins diffraction integral and the method of expanding the aperture function into a finite sum of complex Gaussian functions, an approximate three-dimensional analytical formula for oblique detected laser beam passing through a cat-eye optical lens with center shelter and oblique detector is derived. Propagation characteristics of the distorted reflected beam are performed by numerical calculation. The results show that the incident angle and the oblique angle of the detector create unsymmetrical distortions of the distribution and a certain departure from the return centre. The reflected beam will become a distorted hollow beam because of the existent of the incident angle and the center shelter. The reflected beam gradually evolves into a solid single peak beam with the increase of the propagation distance.