An optical aerial image orthorectification parallel algorithm by Graphic Processing Unit(GPU) acceleration was presented to improve the image real-time processing ability and the serial orthorectification efficiency for massive image data on a CPU. The principle of optical image orthorectification algorithm was introduced, and the parallel processing of orthorectification algorithm was described. To reduce the computational load of GPU execution, the concept of “effective pixel region” was introduced and an improved GPU parallel correction algorithm was designed. Then, the efficiency of the algorithm was improved through configuration options and a memory access optimization. Finally, the algorithm precision was analyzed, and impact of the noise on the algorithm was verified. The experimental results show that the optimized improved-GPU parallel algorithm significantly improves the speed of the correction. When the image size is 5 000×5 000, the speed up is 223 times as compared with the CPU serial algorithm. Although the GPU single precision calculation method and noise interference will cause the serious decline of correction precision, it is still in an allowable error range. As a result, the GPU algorithm implements the orthorectification of optical aerial images rapidly and the corrected images satisfy the need of practical applications.