The invention provides an electromechanical-electromagnetic hybrid simulation method and system. The method includes the steps that a bus with the electromagnetic transient network side connected with a power transmission line meeting a preset condition is determined as a hybrid simulation interface position, wherein the electromagnetic wave propagation delay tau on the power transmission line is larger than the electromagnetic transient simulation step size deltat; the k side of the power transmission line is connected with an electromechanical transient network, and the j side of the power transmission line is connected with the rest of networks of the electromagnetic transient network; the rest of networks of the electromagnetic transient network, the power transmission line and the electromechanical transient network are equivalent to three parts, namely, a part including the j side of the power transmission line and the rest of networks of the electromagnetic transient network, a part including the k side of the power transmission line and an equivalent circuit of the electromechanical transient network and a part including an equivalent circuit of the electromagnetic transient network and the electromechanical transient network; the three parts are solved respectively to obtain the power grid state of the electromagnetic transient network and the electromechanical transient network. By means of the technical scheme, the interface calculation amount is greatly reduced, and the calculation efficiency is improved.