Abstract: Urban grid system with high proportion of air conditioning load has the characteristics of unpredictability and uncontrollability. The sudden rise and drop of city load is becoming the norm. This has a negative impact on the system stability and the situation may get worse when fault occurs in such areas. The reinforcement of city network is restricted by high short-circuit current level and limited transmission corridors, thus the system operators seek more flexible and controllable operation methods. This paper analyses the application of VSC-HVDC technology in city center systems, focusing on providing flexible power support for the connected areas while improving the characteristics of air conditioning load. The effect of VSC-HVDC on the city center system voltage stability is revealed and the capability of MMC for voltage support at different operating conditions is discussed thoroughly.