Abstract: In order to clearly explain the method for judging the imaging direction of prism system，the raytracing

formulas for non-coaxial optical systems are derived，and the imaging processes of plane prism system are

simulated. Through the imaging simulation of a spatial coordinate system，the places difficult to understand about

the judging method for the imaging direction are pointed out. The results show that imaging simulations of prisms are

the most intuitive and feasible method for understanding the imaging direction of prisms. It is not only helpful for

students to understand this judgment method，but also promotes students’keeping this judgment method in mind.

The simulation processes also enable students to profoundly understand various definitions，terms on prisms，which

are not easily understood in the classroom.

Key words: prism system, ray tracing, imaging simulation, imaging direction of prism