In order to measure the refractive index of transparent plate, an improved method based on the Michelson principle is proposed. Using the spatial coherence of low-coherent light sources and distance measurement tools, the distance between optical intervals can be accurately obtained. The optical distances before and after placing the sample and after rotating the sample at a certain angle are measured, respectively. Hence, the refractive index of the optical glass plate can be calculated by using the law of refraction. An iterative algorithm is proposed to avoid directly solving the quaternary equation of one variable and realize fast calculation of the refractive index. By analyzing the measurement errors of distance, angle, and parallelism of the sample, it is found that the refractive index measurement error of the proposed method is better than 5×10 -5. The comparison result with the V-prism refractive index measurement method verifies the correctness of the proposed method.