The image quality of space-based optical payloads is a crucial index for evaluating their imaging performance.Significant differences exist between laboratory test （under ideal conditions） and outdoor practical application （in complex environments）.It proposes a comprehensive evaluation of the ground resolution of the optical payload using bar targets，conducted through testing both in the laboratory and outdoors，with the field test results serving as the final assessment criterion.Practical testing is conducted based on a space-based optical payload.The research results indicate that the platform vibration，atmospheric turbulence，thermal noise，and other factors lead to the actual spatial resolution lower than the theoretical value，with their combined effects causing a system performance degradation of 15% - 32%.These findings provide an important basis for the objective and quantitative evaluation of the practical operational capability of space-based optical payloads and point out the main directions for performance optimization.