Abstract: A low complexity algorithm for designing orthogonal polyphase code based on Hadamard matrix was proposed to decrease the complexity and improve convergence performance of MIMO radar polyphase code design. The algorithm used Hadamard matrix to construct eight-phase code which had a better compromise of phase freedom and processing complexity firstly, the corresponding proofs were presented. Initial code sequences with a certain orthogonality were chosen from them. Then a cyclic algorithm was used as two-step iteration, the cost function computation can convert to FFT and IFFT. By this way, the high complexity caused by computing cost function frequently was overcame. Performance analysis and simulation results indicate that comparing to the existing algorithms, the proposed algorithm can decrease computing complexity and improve the convergence speed effectively, meanwhile it can preserve good autocorrelation and cross-correlation features.