Abstract: In order to fully reflect the transient process brought by distributed generation to the distribution network and the limitation of distributed generation grid connection to the simulation speed of active distribution network, it is urgent to increase the speed of transient simulation. At present, the split-core parallel simulation method is often used to speed up, that is, the distribution network is decoupled by the distributed parameter long line decoupling method. However, due to the short line characteristics of the distribution network, the traditional long line decoupling method is not suitable for distribution network, so this paper improves it, analyzes in detail with traveling wave theory, proposes a short line decoupling method based on characteristic line that adds distributed capacitors, and conducts simulation analysis to verify its effectiveness.