Abstract: Taking TianMa telescope (abbreviated as TM65m) as research object, the variations of primary surface accuracy and antenna pointing accuracy under gravity were researched using the method of combining simulation and experiment. The gravity deformations of structure were analyzed at different elevation angles by finite element software and the corresponding actuator adjustments of primary surface were obtained. The antenna efficiency improves 20% at elevation angle of 35° and 71° when the actuator adjustments were loaded into the active surface system and the primary surface was adjusted. The vertex position of primary surface changed after the gravity deformations of the primary surface were modified. The variation of pointing error is 0.037 99° from 5° to 90° elevation angle when the position variations were converted into the pointing model, which is compared to the modified parameter of gravity error of the real pointing model and the error is 4%. Simultaneously, we found that the gravity of elevation structure and above it leads to elevation axis bend at different elevation angles. The maximum deflection acquired from finite element analysis is 3.2mm. The variation trend keeps in line with measured results of inclinometer, which results in the elevation pointing variation reaching 0.012 14° arc-second. Consequently, reasonable structure design is important to improve antenna accuracy.