Abstract: Modular Multilevel Converter (MMC) is one of the converter topology which is widely used in the VSC-HVDC systems. This converter shows the advantage of high degree of modularity, low output harmonic content, strong scalability,et al.One kind of the modulation strategies is the multilevel PWM strategies which are discovered the disadvantage of low flexibility and easy to produce narrow pulse. Thus, the paper propose a new modulation strategies called frequency conversion integrated PWM (FCIPWM). The method could change the frequency of the carrier wave real-time on the basis of the modulation wave's variance ratio. Thus, the frequency of the carrier wave will increase when the modulation wave change quickly and will decrease when the modulation wave change slowly. Besides, the modulating frequency is low when the modulation wave is in it wave crest so that narrow pulse will be restrained.