To stabilize the DC voltage in a DC distribution network, it is necessary to suppress the double fundamental frequency fluctuation of the active power under unbalanced AC voltages. This paper analyzes unbalanced control strategies of voltage source converters (VSCs). Due to the overcurrent capability of converters, the transmission power limit of VSCs varies with various unbalanced AC voltage conditions. The transmission power limit of the AC side is deduced. Then a numerical method is put forward to calculate the transmission power limit of the DC side. Examples of power transmission under unbalanced AC voltages are simulated by electromagnetic transient simulation software PSCAD/EMTDC. The transmission power limits of VSCs of both the AC and DC sides are necessary for power distribution in multi-terminal DC distribution network. To suppress the fluctuation of the DC voltage, it is necessary to control the active power of VSCs within the transmission power limit of the DC side. This work is supported by National High-tech R & D Program of China (863 Program) (No. 2015AA050104).