In electromechanical transient simulation, there are some problems in sparse triangular decomposition, such as low decomposition efficiency and low parallelism. Based on the implicit trapezoidal integration method, this paper first splits Jacobian matrix according to the characteristics of the Jacobian matrix, and then uses the extended Sherrman-Morrison inverse formula to solve it recursively, so as to avoid sparse triangular decomposition, finally a novel kind of electromechanical transient simulation algorithm is presented. The large-scale synthesis system is tested and analyzed by using high-performance Graphics Processing Unit (GPU). The results show that the parallel algorithm proposed in this paper can achieve better acceleration ratio and good scalability. This work is supported by National Natural Science Foundation of China (No. 51309258).