This paper studies the parallel implicit multi-rate simulation algorithm，builds the basic modeling of this algorithm，and then，the parallel algorithm via the transmission line equation.The result shows that the multi-rate electromagnetic transient simulation algorithm based on transmission lines has higher parallelized levels and efficiency than the existing one.Meanwhile，a criterion for ensuring the stability of the multi-rate electromagnetic transient simulation algorithm based on transmission lines is proposed and proved by theory.Simulation study shows that the parallel implicit multi-rate electromagnetic transient simulation based on the transmission lines might be unstable，but after adjustment of the network division using the stability criterion proposed，the simulation becomes stable.