Abstract: Watermarking synchronization in radio frequency(RF)watermarking system is a technical difficulty.Lacking the ability of frame synchronization recognition, present watermarking synchronization algorithms is inefficiency.In this paper, a method of frame-sync recognition using the technology of watermarking image definition evaluation is proposed.This method uses the corresponding relation between the max value of watermarking image definition evaluation function and frame-sync,establishes independent frame-sync process to slove the problem which needs searching bit by bit in the old watermarking synchronization algorithms,and shortens the time of watermarking synchronization efficiently.The simulation experiments proves the conclusion.