UHVDC hierarchical connection to a system not only improves the voltage support of the receiving end grid but also brings problems such as the complex coupling relationship between different layers of the system. In order to study the operating characteristics of an AC/DC hybrid system with a UHVDC hierarchical connection, this paper examines the ±800 kV Yazhong-Jiangxi UHVDC transmission project. An AC/DC hybrid simulation model with UHVDC hierarchical connection mode is built based on ADPSS. First, the correctness of the electromagnetic transient model is verified. Then the accuracy and superiority of the hybrid simulation model are verified by comparing the simulation results under extinction angle step response of independent control command with the electromagnetic transient model. Finally, the fault simulation of the hybrid model is compared with the electromechanical transient model. Results show that hybrid simulation can accurately reflect the dynamic characteristics of a hybrid system and provide a simulation foundation model. This work is supported by National Natural Science Foundation of China (No. 51577075).