As the application area of time synchronization technology becomes more and more extensive, people not only focus on the accuracy and stability of synchronization, but also start to pursue the speed of synchronization convergence. The digital phase locked loop (DPLL) model is used to achieve the slave clock synchronization with the master clock. The fastest descent method is proposed to reduce the convergence time, by optimizing the filter parameters of the DPLL adaptively. The simulation and experimental results demonstrate that the filter parameters optimization based on the fastest descent method significantly improve the synchronization accuracy and convergence speed of the time synchronization system, finally we achieve an accuracy of 58ps within $100s$ convergence time which compared to manually empirically parameters.