To meet the demands of vehicle-born photoelectric tracking equipment for performance precision, a new support approach using three mechanical legs to support a vehicle was proposed.In the approach, two legs were mounted in the front of vehicle while one leg was mounted on the back according to the layout and weight of vehicle-born equipment. Then the mechanical analysis for the vehicle frame were conducted under three conditions, which consist of that three legs were located on the float land, only the hind leg was located on the slope and three legs were located on the slope. A finite element model was established by using the commercial software MSC.PATRAN. Under the circumstance of three-point support, the deformation simulation was carried out and the simulation results for three conditions were analyzed respectively to testify the re-orientation accuracy of the vehicle frame. Finally, an experiment was designed to examine the re-orientation accuracy of the vehicle frame practically. The experimental results show that the maximum variation of pitch angle is 0.2″ while the maximum variation of azimuth angle is 0.4″, which satisfies the requirements of re-orientation accuracy of the vehicle frame and explains the reasonability of the proposed approach.