The invention provides a photovoltaic power generation relevance index acquiring method. The method includes: collecting and arranging photovoltaic power output historical data of k photovoltaic power stations; performing analysis and regulation on the photovoltaic power output historical data of the k photovoltaic power stations, and finding wrong data and missing data thereof; decomposing the photovoltaic power output historical data of the k photovoltaic power stations into products of clearance theoretical power output Pc (i) and relative power output Pr (i); calculating the relevance coefficients of clearance theoretical power output between every two of the k photovoltaic power stations; calculating the relevance coefficients of relative power output between every two of the k photovoltaic power stations; and outputting a relevance evaluation index calculation result. The method can calculate relevance features of photovoltaic power generation through actual data, and can provide a earlier stage foundation for modeling of photovoltaic power generation time sequences having relevance.