In this paper, a novel position estimation method of prism was proposed for single-lens stereovision system. The prism with multi faces was considered as a single optical system composed of some refractive planes. A transformation matrix which can express the relationship between an object point and its image by the refraction of prism was derived based on geometrical optics, and a mathematical model was introduced which can denote the position of prism with arbitrary faces only by 7 parameters. This model can extend the application of single-lens stereovision system using prism to a more widely area. Experimentation results are presented to prove the effectiveness and robustness of our proposed model.