A method of determining the material of prism by using simple optical experimental instrument is proposed．Taking sodium lamp as light source and using spectrometer to measure the minimum deflection angle，the types of prisms can be distinguished，however the material of prism cannot be determined．Taking mercury lamp as the light source，because the chromatic light will produce dispersion phenomenon after being refracted by the prism，the refractive index can be calculated by using the spectrometer to measure the minimum deflection angle，and the dispersion curve can be obtained． After fitting the dispersion curve with different dispersion formulas and comparing it with the standard dispersion curve of common materials in the same band，the glass composition of the prism can be determined． This method of practical significance is economical，simple，and accurate．