Under conditions of the distorted grid, the traditional phase-locked loop (PLL) cannot accurately extract fundamental positive sequence. For the problem, a decoupled double sinusoidal amplitude integrator phase-locked loop (DDSAI-PLL) is designed. DDSAI-PLL uses a crossing decoupling structure based on sine amplitude integrator (SAI), to achieve the separation of positive and negative sequence components. And the introduction of frequency adaptive module makes DDSAI-PLL have the phase frequency adaptive ability. The working principle of DDSAI-PLL is introduced, its mathematical model is established, and the key parameters are analyzed. Finally, DDSAI-PLL is realized by using DSP and is compared with the traditional synchronous reference frame phase locked loop (SRF-PLL) under the condition of voltage distortion. The results show that the proposed method is effective. This work is supported by Natural Science Foundation of China Youth Fund of Jiangsu Province (No. BK20140586), and Natural Science Foundation for Universities of Jiangsu Education Department (No. 13KJD460007), Suqian Science and Technology Support Program (Industry) (No. H201516), and Scientific Research Fund of Suqian College (No. 2016KY27 and No. 2014KY08).