In order to improve the clean energy absorption capacity of the northwest China power grid and the power supply capacity of the central China power grid, the UHVDC project between Qinghai and Henan and the UHVAC project between Nanyang and Zhumadian will be put into operation in 2020. This paper mainly analyzes the voltage stability characteristics of and improvement measures for the Henan power grid after the above projects are put into operation. The calculation results show that, if the UHVDC project between Qinghai and Henan replaces the conventional power supply, the dynamic reactive power support capacity of the Henan power grid will be reduced, and the transient voltage in the northeast area of Zhengzhou cannot be recovered after AC failure in the near area of part of the load center. It is necessary to put forward requirements for the thermal power units and the synchronous condenser start-up mode in the Henan power grid. In view of the above problems, this paper proposes that the UHVAC project and the UHVDC project should be put into operation synchronously, and thermal power units in the Zhengzhou areas should possess spinning reserve capacity. The effectiveness of the proposal is also verified. This study has reference value for power grid planning and operation and other similar HVDC transmission projects. This work is supported by Science and Technology Project of State Grid Corporation of China (No. 521700190010) “Key Technologies Research and Demonstration of Electrochemical Energy Storage Substation Clusters Applied in UHVAC/DC Hybrid Connected Receiving-end Power Grid”.