As the precision manufacturing industry's requirements for the shape of optical components increase, the calibration of interferometer system errors is becoming more and more important. Among them, using the liquid level reference method as the interferometer system error calibration scheme has the advantages of high precision and low cost. Without considering the influence of external factors, theoretically the curvature of a liquid flat is the same as the radius of the earth, which can be regarded as an ideal plane. However, because the liquid is more sensitive to the environment and not easy to control, how to establish a high-precision liquid level reference is the most important link in the whole process, which directly affects the system accuracy. Due to the fluidity characteristics of the liquid, the previous time-phase shifting method is no longer applicable, so a point source ectopic vertical Fizeau interferometer is used for dynamic measurement, and comprehensively analyze the properties of the liquid and the liquid plate to complete the establishment of the liquid reference.