The Lugu UHV DC transmission system of Northeast China Power Grid is put into operation, its diverse operating modes will increase power flow on the main lines and transmission segments of regional power grids. On the other hand, the reactive power adjustment capabilities of the system will face challenges. To this end, based on the Liaoning Power Grid with UHV DC transmission system, this article establishes the UHV DC voltage static stability evaluation index and stability margin calculation index. By means of the continuous power flow calculation method, the voltage stability of the power grid is analyzed under various typical operating modes and power growth patterns. Weak voltage nodes in the system are identified through calculations, and an additional camera is installed to ensure the system’s reactive power balance. The results indicate that the camera can enhance the voltage stability of the UHV DC transmission system to a certain degree; meanwhile, the voltage stability margin is closely linked to regional load and load characteristics.