Based on a kind of three-phase digital phase-locked loop which the Voltage controlled oscillator is instead of frequency divider, puts forward a new primary passive compound islanding-detection method.Including a new type of active phase shift protection method, a new type of over/under voltage protection based on the principle of phase-locked loop synchronous reference frame .Combined with the other two types of passive detection method at the same time and all depends on the three-phase digital phase-locked loop.The composite detection method have no detection blind area, less impact on the power quality,detection speed meet the requirements ,the structure is simple and easy to realize.Through the model building and simulation in the Matlab/Simulink, verified the method can meet the design requirements and purpose.