Abstract: In order to improve the performance of single-phase software phase-locked loop（PLL）based on synchronous reference frame in power system harmonic distortion,this paper proposes a single-phase software PLL with double moving average filter.The proposed single-phase software PLL adopts double moving average filters to filter the 4k+4（k=0,1,2,）harmonics in the dq axes components of the synchronous reference frame,which is transformed from the odd harmonic component of single-phase voltage.In order to reduce the impact of single-phase voltage frequency-variation on the proposed single-phase software PLL,it applies the weighted average method to mitigate the error of the fundamental wave extraction element due to frequency-variation with the stable frequency from the angular frequency reconstructor module. The experimental results show that the proposed single-phase software PLL is able to obtain accurate amplitude and phase angle of the fundamental under the condition of the presence of harmonics and frequency-variation in the single-phase voltage,plus good dynamic response.