The invention relates to the field of grid-connected photovoltaic power generation performance testing, in particular to a current harmonic index quantification assessment method of a grid-connected photovoltaic power generation system. The current harmonic index quantification assessment method is characterized by including the following steps: (1) performing interval statistics on irradiation intensity; (2) performing statistic analyzing on the timed sampling daytime actually measured irradiation intensity according to the intervals; (3) performing sampling and recording on voltage and amperage of the photovoltaic power generation system on the grid-connection points of the photovoltaic power generation system; (4) determining the measured current harmonic weight coefficients corresponding to the different irradiation intensity; (5) obtaining the harmonic current average value under different irradiation conditions; and (6) calculating the weighting current harmonic value according to the current harmonic weight coefficients of the irradiation intensity intervals. By means of the current harmonics index quantification assessment method, under the condition that the current harmonics of the grid-connected photovoltaic power generation system accord with the standard limiting value requirements, the comprehensive current harmonics of the grid-connected photovoltaic power generation system are obtained in weighting mode when the irradiation intensity changes, and accordingly assessment on performance of the photovoltaic power generation system can be achieved.