Modular Multilevel Converter (MMC), as a new type of topology, has attracted much attention in the research on HVDC system. However, there are some problems such as low anti-jamming capability and unstable output in their internal control systems. According to these problems, this paper improves the systemic control on the basis of original control strategy. The improved control strategy not only can realize independent control of active power and reactive power as well as stable control of the DC voltage, but also can reduce the oscillation amplitude and cut down the recovery time, as a consequence the transient and steady-state performance are improved efficaciously. This paper establishes MMC-HVDC two AC systems and conducts the contrastive simulation analyses between the improved control strategies and original strategies in the Matlab/Simulink. The results verify the correctness and validity of the theory. This work is supported by the National key research and development program of China (No. 2017YFB0902004).