The invention discloses a method for determining the optimal access capacity of renewable energy in a power grid system. A target function for measuring a renewable energy comprehensive consumption level evaluation model comprises two aspects, including a renewable energy consumption amount index and a renewable energy utilization rate index; constraint conditions for measuring the renewable energy comprehensive consumption level evaluation model comprise power supply side constraint and network constraint; a particle swarm optimization algorithm is adopted for solving, the access capacity andoutput of the renewable energy can be adjusted constantly, and the global optimum renewable energy comprehensive consumption level index value is found to obtain the optimal capacity and the optimaloutput of the renewable energy access system under the constraint conditions. By taking the utilization rate of the renewable energy into consideration, a phenomenon of overmuch wind and photovoltaiccurtailment in increasing of the renewable energy capacity can be avoided, and guidance suggestion can be provided for determination of the access capacity of the renewable energy by a power grid planning staff.