Abstract: In the military application field of small reconnaissance UAV（Unmanned Aerial Vehicle）, general synchronization acquisition technology of DSSS has been difficult to meet the current requirements of low speed and low CNR(Carrier to Noise Ratio). In this paper, a synchronization acquisition algorithm named Double FFT Combine with Autocorrelation for Small UAV is designed and simulated for this application. The correlation peak is obvious, and it is not affected by the residual carrier and accumulation time. The noise interference is small and the frequency estimation is accurate. This effectively promotes the signal reception stability of small UAV in military applications.