The current research on power system cloud computing mainly focuses on the construction of large-scale computing centers and the design of related scheduling strategies, and there is no relevant application research on the combination of cloud platform and power simulation software. In order to explore the improvement effect of cloud computing technology on real-time computing performance of electromagnetic transient simulation software ATP-EMTP when calculating large-scale power grids, we combine cloud platform with ATP-EMTP and use simulation models of different scales to compare the computing efficiency of the simulation software in local computer and cloud platform. After actual comparison, cloud platform can improve the computing efficiency of ATP-EMTP to some extent, but because of the limitation of the software itself, cloud computing technology cannot essentially improve the real-time computing performance of ATP-EMTP. From conclusions obtained, the corresponding research direction is proposed on how to improve the real-time computing performance of ATP-EMTP through cloud computing technology. This work is supported by the National Natural Science Foundation of China (No. U1766208).