Symbol synchronization is a key technology for synchronous demodulation of digital modulation signals. Aiming at the limitation of timing error detection and long timing time in the closed-loop Gardner timing recovery algorithm, the timing error detection method is modified, and an improved method of adding gain control processing is proposed. The simulation results show that the improved algorithm can capture timing error of multi-level modulation signal, significantly reduce timing errors and shorten timing time. The steady-state timing jitter is an order of magnitude smaller than the classic loop. The timing recovery of MQAM signal and MPSK signal can be completed well, which proves the good applicability of the improved algorithm.