The invention discloses a roof type photovoltaic array equipment investment optimization method, which comprises the following steps of: predicting medium and long-term power generation quantity according to the following formula: W = etaTp, wherein the eta is a correction coefficient, and comprehensively considering efficiency loss and transmission loss; Wherein T is the annual average utilization hour number; Wherein p is peak power generation power, the correction coefficient is adjusted by adopting a method of combining the existing data of the automatic station for correcting the coefficient, and the correction coefficient is uniformly calculated into an efficiency loss coefficient and is considered; Wherein the annual average utilization hour T is determined by the annual average sunshine duration and the average irradiance of the meteorological bureau. By the adoption of the technical scheme, roof resources of different environments, different regions and different conditions are obtained, so that reasonable input is conducted, roof equipment input and the maximum cost performance of generating capacity are achieved, and the maximum benefit of building surface photovoltaic power generation is achieved.