Abstract: The clamping and machining force model are established and the milling force value is calculated based on the milling program of the turning pedestal datum plane. By using the finite element simulation method, the clamping simulation model and machining simulation model are established respectively, and the deformation by force of the datum plane are simulated and analyzed. The technological test method is adopted to verify the simulation results under the same working condition. Analysis shows that the use of jacks can effectively reduce the effect of gravity on the deformation of the base of the turning gear when clamping. The jack exerts a force of 4 000 N at position ③, and the deformation is reduced by up to 85%. In the simulation, the maximum datum level deformation value is 0.010 915 mm. The maximum deformation of the reference plane in the test is 0.02 mm, which is less than the parallelism requirement of the reference plane of 0.04 mm.