The invention relates to an automatic net-dividing method for large-scale electromagnetic transient simulation of a power grid. The method comprises the following steps: automatically dividing nets with the unspecified number of sub-nets and automatically dividing nets with the specified number of sub-nets. The parallel processing technology is applied to the electromagnetic transient simulation of the power system so that simulation speed is increased and the requirements for real-time and super real-time simulation of a large-scale power system are satisfied. By taking nodes connected between networks as the boundary points of the sub-nets, the overall simulation network of the power system is naturally divided into all sub-nets. According to the precision need, the simulation steps of different networks can be determined. The automatic net-dividing method has the following beneficial effects: no decoupling element is required for network dividing which is simple and clear and highly universal at fast speed; and electromagnetic transient subnets containing VSC precision models at different speed and step lengths are parallelly stimulated.