The cold shield in the cooled infrared detector usually adopts vanes of right angle structure. The stray light reflected by the sidewall of the vanes can reach the focal plane directly, resulting in a significant decrease in the imaging quality of the detector. Based on the theoretical analysis of the vane structure, an optimized structure of the vane sidewall which suppresses stray light is proposed. The LightTools software is used to simulate and analyze the cold shield before and after optimization. The analysis results show that the total power of stray light decreases by 71.6%.Through experimental verification, it is found that the average response non-uniformity of the detectors decreases by 27.1%, and the imaging effect is significantly improved. The results show that this optimized structure is very effective in suppressing stray light.