The invention relates to a modeling method for an electromechanical transient model of a string photovoltaic inverter. The modeling method comprises the steps of establishing a control model and an output current model. According to the modeling method provided by the invention, deep analysis on the working principle and the control strategy of the string inverter is performed, and then the key external characteristics of the inverter are extracted; by combination with the characteristic of the electromechanical transient simulation of an electric power system, the electromechanical transient model with high simulation speed and high convergence is established; the model established by the method provided by the invention has the advantages of clear structure, definite physical meaning and easy realization; and therefore, the dynamic response external characteristics of the string photovoltaic inverter in suffering from disturbance and faults can be simulated accurately, and the grid-connection analysis requirement of a photovoltaic power station based on the string photovoltaic inverter can be satisfied.