Since the Yazhong UHVDC and Huazhong UHVAC ring networks are connected to Jiangxi power grid, power grid characteristics have changed completely. Transient stability constraints become the main reason of constraints for operation and control of Jiangxi power grid. Under the background of AC-DC hybrid, it has practical significance that studying deeply on the transient stability level and its influenced factors of Jiangxi power grid. Based on the PSASP program, this paper establishes a voltage level above 220 kV system and a ±800 kV layered DC model in Jiangxi power grid. It simulates and analyses typical faults in DC systems, typical faults in DC near-area AC systems, and effects of AC ring network on grids transient stability, presenting control strategies and countermeasures to improve the level of transient stability, which lays the foundation for safe and stable operation of UHV AC/DC access to Jiangxi power grid. This work is supported by National Major Research and Development Program of China (No. 2018YFB0904001).