The absolute test method of liquid surface usually uses a high-viscosity liquid plane as a reference for calibrating the flatness of optical flat, which has a long stabilization time and recovery time after disturbance. An absolute test method of dynamic liquid surface is proposed, which uses a dynamic interferometer to measure the dynamic surface shape of a low-viscosity silicone oil surface and uses its average value as a reference surface for calibrating the systematic error of the interferometer. Based on the principle of multi-dimensional modal analysis, a liquid plane fluctuation model is established and simulations are carried out using the finite element method. The simulation results show that the dynamic liquid surface fluctuates vertically based on the standard liquid surface corresponding to the radius of the earth, and the amplitude is in the form of a cosine function. The mean value of the residual error of the liquid surface flatness over the sampling time can be controlled to the order of 10-3nm. Experiments were carried out on a Φ300mm vertical dynamic Fizeau interferometer on silicone oil of 0.65Cst viscosity and 3mm liquid thickness with a sampling time of 30s.The results of the dynamic interferometric calibration of a low-viscosity silicone oil are compared with the stable absolute test results, and the surface distribution is consistent, with a deviation of λ/63 in PV and λ/400 in RMS. The simulation and experimental results demonstrate that the interferometer system error can be calibrated with low viscosity silicone oil interferometric mean results.