The invention discloses a photovoltaic high-duty-ratio power grid UPFC application optimization method and system based on an MFO algorithm. The method comprises the steps: obtaining a UPFC control model; according to the UPFC control model, determining UPFC optimization parameters and obtaining an optimization objective function; and optimizing the UPFC optimization parameters based on the MFO algorithm. Population initialization, a flight mechanism and flame extinguishing rules of the MFO algorithm are improved, the global optimization capability of the algorithm is improved, and the convergence rate is increased; and the effectiveness of the proposed method is verified through joint simulation of MATLAB and PSD-BPA, so that the transient voltage support capability and the damping poweroscillation capability of UPFC equipment to a power grid are improved.