The invention discloses an island detection judgment method of a distributed photovoltaic power generation system, and belongs to the technical field of island detection of photovoltaic power generation systems. By separating component coefficients of fundamental waves, third harmonic and quintuple harmonics in network voltage signals, time domain and frequency domain analysis and calculation areperformed, on the basis of dynamically tracking the setting for judging the threshold, such as sudden changes of determination thresholds and amplitude thresholds, existence of an island detection blind region is avoided to the maximum extent, and the detection and determination precision is improved.