In order to solve the problem of complex computation and slow response of the grid voltage lock algorithms currently, this paper has proposed the grid voltage synchronous signal detection algorithm based on the amplitude calculation. Its aim is to accelerate the response speed of the algorithm and achieve a fast track to grid voltage synchronous signal when the grid voltage is good. Firstly, this paper has introduced the principle of the grid synchronous signal detection algorithm to meet the requirement of speediness. Then, three grid voltage amplitude calculation algorithms were given, and they were compared and analyzed in detail. Finally, the simulation and experiment have verified the effectiveness of the three algorithms to detect the grid voltage synchronous signal.