Space-borne two-dimensional turntables are the main bearing mechanism of space cameras and other optoelectronic equipment, and the U-frame is the key supporting part of these turntables. In order to optimize the structure and lightweight design of the U-frame of the two-dimensional turntable and to develop a lightweight two-dimensional turntable with a high load-bearing ratio, we design a U-frame for the space two-dimensional turntable based on Carbon Fiber Reinforce Plastics (CFRP). First, a variable cross-section tubular structure U-frame was designed using carbon fiber composites instead of titanium alloy material considering the manufacturability. Then, according to the finite element modeling method based on the lay-up process, the carbon fiber U-frame was subjected to finite element modeling and simulation analysis. Then, a prototype U-frame was fabricated, and modal tests verified the accuracy of the finite element model. Finally, a three-level optimization method combining theoretical analysis, genetic algorithm, and the finite element method was proposed to optimize the design of carbon fiber U-frame ply angle, ply thickness, and ply sequence. The results indicate that the vibration patterns of the U-frame obtained from the modal test and simulation are identical and that the frequency difference is less than 5%. The initial design of the carbon fiber U-frame is 45.7% lighter than the titanium U-frame. Through the secondary optimization of the composite layup, the U-frame is further reduced in weight by 13.8%. Additionally, the intrinsic frequency of the U-frame is improved by 10.14%. It can be concluded that the composite modeling and optimization methods used in this paper are correct, and the designed carbon fiber U-frame meets the lightweight design requirements of space-born two-dimensional turntable.