The invention relates to a distributed photovoltaic power generation operation mode optimization design method and system. The method comprises: calculating the actual power of a distributed photovoltaic power generation system in a statistical period according to the actual illumination intensity, the standard power and the standard illumination intensity of the distributed photovoltaic power generation system in the statistical period; enabling the distributed photovoltaic power generation system to use 100% of the power generated by itself if the actual power data is less than or equal to load power corresponding to the statistical period; and transferring excess power to a power grid after a user load requirement is satisfied if the actual power data is greater than the load power corresponding to the statistical period. The method optimizes the power supply control process of the distributed photovoltaic power generation system based on the actual illumination intensity and the actual power in the corresponding statistical period, improves the power supply control accuracy of the distributed photovoltaic power generation system, and optimizes and rationalizes the designed distributed photovoltaic power generation operation mode.