Abstract: A vector formula method based on reflection law was used to trace three-dimensional light propagation direction in a complex system. The direction of the light reflected by each side of Pechan prism was calculated, Jones matrix of the reflected plane and the transfer matrix between planes were established using Jones vector, and the distribution of polarization state on image surface was obtained when linearly-polarized parallel light passed through Pechan prism. There were two elliptically polarized beams with different azimuth angles from two roof surfaces, and the angles were dependent on the oscillation direction of incident linearly-polarized light. The distribution of polarization state on image surface of Pechan prism was tested with Stokes parameter measurement. The experimental result agrees with theoretical analysis and indicates that the polarization effect of Pechan prism results in non-uniform distribution of polarization state of the exit light.