When the traditional separation methods for the positive and negative sequence separation is poor versatility shortcomings in unbalance, we propose a new approach based on improved SPLL for separation of the positive and negative sequence component. It uses second order generalized integrator better filtering effect for high times and positive and negative sequence cascade characteristic of DSC harmonic elimination by αβ transform and dq transformation and use the software phase-locked loop principle to lock the frequency of the grid and feedback to the second-order generalized integrator and negative sequence cascade of DSC to separate the positive and negative sequence component grid. This method can be fast and accurately separate the grid positive and negative sequence fundamental component in grid voltage symmetrical, asymmetrical fault and power grid voltage frequency change, which can be reliable support control signal for power electronic converter control system .We proved the proposed method is feasible and effective by using MATLAB/Simulink software simulation results.