The detection method based on traditional instantaneous reactive power theory need to rely on the grid voltage phase-locked loop (PLL), but that the network side voltage waveform distortion, frequency fluctuations and other adverse conditions will have great impacts on the detection accuracy .We propose an improved control solution , which is based on virtual flux orientation method to get the phase angle signal as same as the grid voltage frequency and phase, through a low-pass filter at the input of cross-compensation link , which is set to avoid integrator saturation phenomena , and thus to improve the flux observer accuracy. In the rotating coordinate system, there are the coupling phenomena between d-axis and q-axis in the three-phase shunt active filter mathematical model , and we use state feedback decoupling control and grid voltage feed forward decoupling control method , which can avoid the grid voltage disturbance effects and the use of quasi-resonant controller compensate characteristic frequency harmonics. Simulation results verify the effectiveness of the control solution.