In order to improve the temperature adaptability of vehicle-borne beam expander system, a structural optimization method is proposed to directly deal with optical wavefront aberrations. After sensitivity analysis, root mean square (RMS) value of the optical wavefront aberration can be calculated from the strain of the finite element nodes through homogeneous coordinate transformation. Taking the minimum wavefront aberration as the optimization objective, an optimized topology is obtained. According to the topology of material, the frame is divided into blocks, and optimized secondly in the form of size optimization. Finally, a manufacturable structure with good temperature flexibility is obtained. When the thermal load is -50 ℃, the wavefront aberration RMS value is reduced from 0.728 λ to 0.196 λ, λ= 632.8 nm. And in the range of ±50 ℃, the optimized wavefront aberration RMS value is about 1/4 times as large as that before optimization at the same thermal load conditions.