For the actual demands of the aerial electro-optical detection system, firstly, the qualitative and quantitative factors for evaluating the optical image quality were analyzed from the perspective of image information, an image definition evaluation method based on similar feature region extraction was proposed to achieve the matching between the subjective feeling and objective evaluation of the image definition. Then, from the perspective of the optical evaluation of imaging system, the optical transfer function, aberration, transmittance and other factors affecting the imaging quality were analyzed, and according to the multi-band long focal reflective optical system, the experimental results were verified. Finally, combined with the requirements for engineering practice to improve the imaging quality, several aspects that should be given more attention in the development of optical imaging system were pointed out. And for the multi-band long focal reflective optical system, some specific parameter suggestions were given.