Voltage source converter (VSC) based HVDC is a hotspot in the study and application of HVDC in recent years. However, the AC/VSC-HVDC parallel transmission system has made the distribution of the power flow more complex in the power networks. As VSC-HVDC can control its active and reactive power flow independently, it would be useful to improve the efficiency of the AC/DC parallel transmission system by studying the optimal power flow in parallel AC/DC systems. This paper presents a multi-objective optimization method for active power flow in parallel AC/DC transmission systems. The objective functions are established considering the constraints of multiple objectives. Based on the fuzzy theory, the objective functions are specified to their corresponding membership functions, and then the optimal assigned value of active power of the AC/DC parallel transmission system can be found out. Finally, the result of the calculation example verifies the feasibility of the proposed method. Compared to the method of setting the active power flow in the AC/DC parallel system based on operating mode and operating experience, the multi-objective optimization method can not only reduce the network losses but also ensure the safety and stability of the operation of the AC/DC parallel power systems.