In view of the lack of space objects' attitude estimation based on space-based optical observation, this paper applied the Unscented Kalman Filter (UKF) to the Geosynchronous Orbit objects' attitude estimation based on space-based optical observation. Taken the Optical Cross Section (OCS) instead of magnitude as observed variable, linearizing and simplifying the observation equation. In addition, an OCS observation model based on the improved Phong model was established, which improves the description ability of the observation equation. And the angle was used as the input of the model, which greatly simplifies the calculation and enhances the real-time capability. Finally, compare the attitude estimation of the Kapton cuboid and the Lambert cuboid, the effectiveness of this method is verified, and the attitude estimation of the regular hexagonal prism and eight prism is also carried.