Time synchronization is an important theoretical research in wireless sensor networks. The users can know accurately know the information in the monitoring area, only when the sensors have a consensus clock. An innovative distributed time synchronization protocol, called GCTS(group consensus time synchronization), was proposed for largescale wireless sensor networks. Each sensor node collects the clock information of the neighbors. The sensor update the clock information according to the result of calculation using group consensus protocol. The advantage of the protocol is fully distributed and it has simple calculation, fast convergence rate and low energy consumption. At the same time, the proof for the convergence of the proposed protocol is carried out using Lyapunov stability theory and graph theory. Finally, the proposed protocol for largescale wireless sensor networks is implemented in Matlab, and the experimental results meet the expected analysis.