Abstract: Complex image registration is one of the most important steps during the process of interferometric signal processing, and its efficiency directly affects the performance of interferometric signal processing system. In order to improve the efficiency of complex image registration algorithm, we propose an optimized complex image registration algorithm for interferometric synthetic aperture sonar (InSAS) in shared memory environment. Firstly, after analyzing the characteristic of calculation and parallelism of each processing step for complex image registration, an optimized computation method for coarse registration and refine registration is proposed for the massive sliding operation based on the coherence of data in adjacent windows. Then, in order to make full use of multi-core computing resource to accelerate the process of complex image registration, OpenMP instructions are used to parallel design and task allocation for coarse and refine registration, complex image interpolation and wrapped phase extraction. Finally, the correctness and efficiency of the proposed method are verified by the parallel complex image registration for InSAS.