With the expansion of power grid scale, transimission corridor resources become more and more scarce, the possibility of fault occurrence for two crossing transmission lines is intensively increasing. This paper presents a new electromechanical transient simulation method for this kind of fault. Firstly, elimination processing are carried out for both the faulty order network voltage equation and the boundary condition equation in order to obtain additional positive sequence impedance matrix of fault node, and the matrix is processed symmetrically. Then the additional positive sequence impedance matrix of fault node is extended to faulty line nodes. According to the additional positive sequence impedance matrix of faulty line nodes, corresponding transient data card is generated and electromechanical transient simulation method for two crossing transmission lines is proposed. Finally, by using the data of an actual power grid, electromechanical transient simulation is carried out for the fault of two crossing transmission line and ground fault of two crossing transmission line. The simulation results verify the correctness of the proposed method.