The invention discloses a harmonic wave type island detection threshold setting method, and belongs to the photovoltaic power generation system technical field; the method comprises the following steps: obtaining load impedance through a load capacity; approximately obtaining system impedance through a short circuit capacity; converting obtained impedance into harmonic wave impedance of the corresponding frequency, thus obtaining island back and forth harmonic wave impedance change conditions, obtaining island back and forth harmonic wave voltage change multiple theory reference values, and setting a motion threshold. The invention provides the harmonic wave type island detection motion threshold setting reference method, thus improving the practical engineering value.