Abstract: In high-precision interference detection, the calibration of interferometer system errors was important. According to the structural characteristics of the vertical Fizeau interferometer, the liquid reference plane was used as a reference to compensate and calibrate the self-weight deformation and clamping deformation of the reference flat crystal, and calibrate its system error. Theoretically, the curvature of the liquid surface and the radius of the earth were the same, which can be regarded as a plane reference to calibrate the system error of the vertical structure interferometer. For the Φ300 mm vertical Fizeau interferometer, the influence of different liquid viscosity, thickness, interference cavity length and temperature was studied, and a reliable liquid reference plane reference was constructed. Through the liquid reference plane, the interferometer was guided to refer to the installation and calibration of the reference flat crystal, and its system error was compensated. The accuracy of the interferometery reached 0.035λ, which was better than λ/25. In order to further verify the reliability and accuracy of the liquid reference plane, repeatability experiments were carried out, and the liquid reference plane of Φ400 mm and Φ450 mm were used for comparison test. The deviation of the two calibration results was better than λ/100 (6 nm). The reliability and accuracy of the liquid reference plane were verified.