A novel islanding detection method based on Power Controlling is presented in this paper. The method continuously perturbs the reactive power supplied by dispersed generation systems while simultaneously monitoring the point of commoncoupling (PCC) voltage and frequency. When in grid-connected scenario, the voltage and frequency of PCC is insignificant; however, once the islanding event takes place, the frequency of PCC will be change own to the change of output reactive power. After it is over 4 cycles continuously, then the active power of dispersed generation systems is reduced to 80%, now a drop in voltage positively confirms islanding. Algorithm of the method is simple and confirmed by simulation with MATLAB.