The invention provides a combined high-voltage DC circuit breaker suitable for a DC power grid and having a power flow control function and a control method thereof. The circuit breaker comprises an electric reactor, an isolating switch, a normal through-flow branch and a fault cut-off branch. The normal through-flow branch is formed by connecting an ultra-fast isolating switch and a modular multi-level power flow controller in series. The fault cut-off branch is formed by connecting a plurality of main circuit breaker sections with bidirectional through-flow capacity in series and in parallel. According to the invention, a DC power flow control function is integrated into the combined high-voltage DC circuit breaker, so that the combined high-voltage DC circuit breaker has DC power flow control capability and DC line fault processing capability at the same time, and the functional diversity and operation flexibility of equipment are improved.