In order to calibrate the nonlinear error of laser interferometers and high-precision displacement sensors with an accuracy of nanometer order, the linearity, stability and measurement range of the beat frequency Fabry-Pérot interferometer developed by National Institute of Metrology and Tsinghua University should be improved. Based on analysis of the influences of factors, such as the change of air refractive index and the tunable range of He-Ne laser, a vacuum system that airproofs the interference light path is designed and built, and a diode laser with a large tunable range is used to take place of the He-Ne laser. The experimental results show that the nonlinear error of the system in the range of longer than a quarter of the wavelength is reduced from 8.93 nm to 1.19 nm.