In order to accurately study the dynamic characteristics of HVDC power transmission system, aiming at the ± 500 kV HVDC project from Jiangling to Echeng, a hybrid modelling method based on advanced digital power system simulator (ADPSS) is proposed to carry out electromechanical-electromagnetic transient simulation. By means of circuit equivalent transformation method, the calculation principle of hybrid simulation is analyzed. Then the method for constructing electromechanical model and electromagnetic model is expounded. On the basis of the built hybrid model, the ground faults happening at AC buses connecting to rectifier and inverter are respectively simulated, and the comparison with the general electromagnetic model simplifying the simulation scale of AC system is implemented. The simulation results show that the modelling method for HVDC power transmission system based on ADPSS is valid. It can reflect the dynamic characteristics of HVDC system more precisely than pure electromagnetic model, and enhance the accuracy of simulation model.