In digital receivers, symbol timing synchronization is one of the most important process for signal demodulation, and directly affects the performance of the demodulation algorithm. In this paper, an improved united estimation algorithm for the symbol timing synchronization of QAM is presented, based on the maximum mean power estimate algorithm. In this algorithm, a simple interpolation filter is used to make the signal double interpolated first, and then the maximum mean power estimate algorithm is used to find the maximum mean power point as the best sample point. High estimation accuracy without high sampling rate and using complex algorithm can be ensured in low signal-to-noise ratio. The simulation results of this new algorithm indicate that this proposed scheme has low algorithm complexity, high estimation accuracy and strong anti-interference ability, and a fast symbol timing synchronization of QAM can be implemented.