Abstract: In this paper, the random scenario simulation method was employed to describe the stochastic outage accidents of units and transmission lines as well as load prediction errors. Additionally, a stochastic expansion planning method of AC/DC hybrid transmission network was proposed based on Benders decomposition. Firstly, the comprehensive cost objectives of AC/DC transmission line investment cost, loss of load cost and system operation cost were established. The mixed integer linear programming model of AC/DC hybrid transmission network was decomposed into the main planning problem and the subproblems of reliability verification and economic scheduling through Benders decomposition. The simulation results of the six-bus system and the modified IEEE-118 bus system demonstrate that, in comparison to the AC transmission system, expanding the DC transmission line yields greater cost savings. The selection of an AC/DC transmission line can enhance the controllability and economy of the transmission power flow, thereby reducing load loss in the DC line.