Abstract: Given the complex harmonic conditions at the grid connection point of distributed photovoltaic power plants and the need for accurate identification of harmonic sources, this paper proposes a harmonic source localization method based on maximum power point tracking (MPPT) of photovoltaic power plants. First, when harmonic values at the grid connection point of a distributed photovoltaic power plant exceed the threshold, then real-time data is collected on the maximum power value tracked by the MPPT module of the grid-connected inverter, along with corresponding grid-connected current values, converter duty cycle, and other electrical parameters. By actively adjusting the converter duty cycle to modify the grid-connected power of the photovoltaic power plant and dynamically comparing the harmonic current values at the monitoring points with the grid-connected current values of the power plant, the method enables the identification and efficient localisation of harmonic sources at the grid-connection point of the photovoltaic power plant. Experimental results demonstrate that this method can effectively distinguish harmonics generated by the photovoltaic power plant from those produced by other loads within the distribution network, significantly enhancing the targeting and effectiveness of harmonic mitigation for distributed photovoltaic power plants.