The larger the telescope aperture, the structural rigidity of the requirements for tracking aircraft higher, for photo-electric theodolite. Photo-electric theodolite’s aperture is designed related to tracking frame, so tracking frame is more and more attention. In this paper, U-type track frame horizon as an example, the two key components are designed with square steel tube truss structure. By finite element design and modal analysis, solving the inherent resonant frequency. In the last, we used to design in steel casting and welding methods. This paper discusses a new design of welded steel pipes. And it has a modal analysis. So that it has a greater carrying capacity and higher stiffness and lighter, more abundant reserves of torque. The mechanical resonance frequency is 78 Hz for tracking frame after a vibration test and sweep test.