Based on optical collimation, a non-contact three-dimensional small angle measurement method is presented by using a pyramid prism as a cooperation target. A retrieving algorithm which calculates simultaneously the pitch, yaw and roll angles is proposed according to the spot centroid. Based on this, a measuring system is designed to finish modeling and simulation experiments. Simulation experiments show that the method has the characteristics of long working distance, high accuracy and decent range, and has good application value in engineering.