Abstract: As the attitude sensor with the highest absolute accuracy, the star tracker was widely applied in the most remote sensing satellites recently, and its performance is an important element to influence geometric loacation accuracy of the remote sensing satellite image. A raw stellar image processing project is firstly designed for the domestic APS star tracker loaded on the first civilian high-resolution stereo mapping satellite-ZY-3. The raw stellar images captured by the domestic APS star tracker were downlinked to the ground for post-processing. This attitude post-processing project has taken full advantage of all observed data in a period of time and sufficient computing resource on the ground, compared to the on-orbit real-time processing. And the key technologies such as the stellar image pre-processing, guide stars selection, star identification, and on-orbit calibration of the stellar camera et.al had been improved and optimized. On this basis, the post-processing system for the APS star tracker of ZY-3 satellite was implemented and applied for the absolute attitude determination based on the raw stellar images. The real-time stellar images from the APS star tracker were downloaded for test verification. The experiment result indicates that the post-processing system based on the stellar images has the characteristics of high automation and reliability. The random pointing error of optical axis was regarded as the attitude accuracy of the APS star tracker. The post-processed attitude accuracy achieves 1.82 arc seconds(1σ), which is better than that of real-time processed 2.18 arc second(1σ). This attitude post-processing system will provide technical support for the daily operational running for the raw stellar images of ZY-3 satellite.