Based on the optimization of the optical material and internal reflection angle, we designed a model of improved Fresnel prism that is insensitive to the angle of incidence. In this device, the incident light is reflected twice at the same internal reflection angle on the interface between two kinds of glass and the air. So the changes of retardation caused by reflection can compensate each other. The calculation shows that the departure of this kind of phase retarders is less than 0.36° when the angle of incidence changes between -2°　and +2°.It reserves the merits of normal incidence and normal output in archetypal Fresnel prism, and brings convenience in the operation.