The principle of beam splitting of spectrometer based on the combination of two Wollaston prisms and a half-wave plate is presented. The propagation track of light wave in the combination is analysed by wave normal-tracing method at random incidence angle and the formulas of the path difference between the e and o wave normal are deduced. Computer simulations are carried out to explain why the combination can increase the field of view of spectrometer. The results will provide a very important theoretical basis for the study of polarization interference imaging spectrum technology and the development of static large field of view polarization interference imaging spectrometer developed by us.