In the existing stereo image synthesis algorithms used in the auto-stereoscopic display，the inclination
angle of image synthesis is inflexible，the synthesis process is slow and the effect is poor．Therefore，we propose a novel algorithm named as self-adaptive stereo image synthesis algorithm，which adjusts the inclination angle during the process of image synthesis based on the theory of binocular stereo vision used in the auto-stereoscopic display．In the algorithm，a novel law of judgment named the law of judgment by the first column sub-pixels is proposed and then the inclination angle of the image to be unmapped is adjusted automatically according to the inclination angles of the partial mapped images during the process of image synthesis，so that the judgment number of sub-pixels can be decreased and thus the synthesis of stereo images can be sped up． Simulation results demonstrate that the proposed algorithm is suitable for the auto-stereoscopic display equipment with any inclination angle of parallax barrier and can make the synthesis more reasonable．