Abstract: Since conventional refractive index measurement methods such as least deviation angular test method, auto-collimation method and critical angle method require a sample prism specially made for such measurement, they are time-consuming and complicated. on-contact measurement of refractive index based on parallel surface plate was used to ensure the integrity of the material to be measured and achieve automatic measurement.The results show that the method is easy to realize automatic measurement and its accuracy could be achieved by choosing apropriate measurement angles. The obtained rotation angle accuracy is a=0.003(10), the guide precision is L=0.000 8 mm and the measurement accuracy of parallel surface plate thickness is d=0.001 mm .