Abstract: In view of the inadequate performance of islanding detection of the traditional Sandia frequency shift（SFS）method for multiple grid-connected inverters,an improved SFS algorithm based on adaptive parameters is proposed.The algorithm uses the digital correlation theory to detect the phase difference between the voltage of the point of common coupling and the output current of the inverter.According to the phase difference,the initial chopping coefficient cf0 and positive feedback gain Kof the SFS algorithm are adjusted accordingly with respect to the detection error of frequency and load quality factor,so as to eliminate the failure of islanding detection caused by the dilution effect and high quality factor of load.Theoretical analysis and simulation experiment results show that the improved SFS algorithm is evidently superior to the traditional algorithm in the case of dilution effect and bad load conditions.