The math modeling of the double-loop speed control system for the single-phase type LCL filter is established. The stability of the system is analyzed by using frequency-region method and Ziegler-Nichols method. The internal and external parameters are tuned preliminarily. Aiming at the shortages existing in the traditional PI parameters tuning method, the genetic algorithm is used to optimize PI regulator parameters. It makes use of the operators of choice, crossover and mutation in genetic algorithm to get fine PI adjustor parameters. The rise time and the over-shoot are added in the fitness function as part of the adaptive evaluation. The Matlab/Simulink simulation shows the optimization of controller parameters can suppress the grid current harmonic effectively, and the system has favorable stability and dynamic performance. This work is supported by National Natural Science Foundation of China (No. 61601256) and National Key Research and Development Program of China (No. 2016YFB0900903).