Abstract: When the feedback structure based on COSTAS loop is used in carrier synchronization of OQPSK signal with large frequency offset, the locking time is so long that feedback structure poorly fits for burst signal. To resolve this problem, this paper designs an improved algorithm based on the power spectrum of OQPSK signal and the feedback structure. Simulation results show that the performance of the improved algorithm is better than the traditional COSTAS loop, and the improved algorithm has a short locking time and low bit error rate which almost attains Shannon capacity under that power-to-noise ratio is higher than 6 dB.