The invention is applicable to the technical field of renewable energy power generation, and provides a method and a device for determining the photovoltaic access capacity. The method comprises the following steps: linearly fitting the operating voltage and the load active power measured by a preset station area meter; The minimum load active power and the load active power corresponding to the upper limit value of the operating voltage are determined according to the fitting curve, and the maximum photovoltaic access capacity is further determined. Determining a voltage value of the photovoltaic access preset station area according to the maximum photovoltaic access capacity, and determining a voltage proportion coefficient according to the voltage value of the preset station area substation and the voltage value; According to the load active power and voltage proportional coefficient corresponding to the upper limit value of the operating voltage, the upper limit voltage of the preset substation is obtained. If the upper limit voltage is greater than a preset upper limit voltage threshold, the maximum photovoltaic access capacity is modified according to the upper limit voltagethreshold, thereby avoiding the occurrence of light abandonment phenomenon and providing technical support for reasonable photovoltaic planning and improving photovoltaic utilization rate.