In order to realize the goal of “dual-carbon” strategy, the proportion of new energy in the new power system continues to rise, and the AC-DC hybrid architecture highlights the voltage stability problem. Based on an actual project case in Northwest China, this study improves the standard example of Chinese Academy of Electric Sciences (CEA) to construct a voltage instability model of AC-DC grid with new energy penetration rate of more than 50% and 100 nodes. Relying on the cloud simulation platform CloudPSS, a three-phase permanent N-2 fault is set up under the basic operation condition, and the transient voltage sensitivity study is carried out by adjusting the DC power level and the new energy penetration rate. The simulation results show that: every 150 MW reduction in DC power can increase the transient stability margin of the system by 12.7%; every 10% increase in new energy penetration will lead to a 23.4% extension of the voltage recovery time; the proportion of synchronous unit output is positively correlated with the voltage stability coefficient (R2 = 0.89). The research results provide theoretical support for the new type of power system voltage stability analysis, and have engineering guidance value for improving the level of power grid security operation.