Abstract: Drift angle distribution of elliptic solar synchronic orbit was discussed with an image simulating method based on orbit elements and TDICCD imaging mechanism. Image quality was evaluated based on PSF distribution of the simulated final image, and drift angle calculation was carried out. Results show that drift angle of elliptic orbit is linear to half -major -axis and cubic polynomial to orbit eccentricity when argument of perigee is 0. Image quality distribution aimed at KH-12 camera's critical inclination orbit due to angle drifting in case MTF 0.95 was discussed. Results show that smaller drift angle at neighborhood of the perigee of elliptic orbit and higher image quality can be achieved under same integral number.