The invention relates to a modulation method and system for a modularized multi-level current converter with mixed sub modules. The modulation method comprises the steps of determining modulation wave of each sub module in each phase bridge arm according to each phase to-be-output instruction voltage waveform, wherein the modulation wave of each sub module comprises the modulation wave of a half-bridge sub module and the modulation wave of a full-bridge sub module; performing comparison between the carrier wave of each sub module and the modulation wave of each sub module in each phase bridge arm to generate control signals for controlling the input or cut-off of each sub module in each phase bridge arm separately; and performing output voltage waveform superimposition on the sub module input in each phase bridge arm to obtain the output voltage waveform of each phase bridge arm. The modulation wave of the half-bridge sub module is used for modulation with the carrier waver of the half-bridge sub module; the modulation wave of the full-bridge sub module is used for modulation with the carrier waver of the full-bridge sub module, so as to realize the accurate modulation on the carrier wave and the modulation wave of the mixed sub modules, therefore, the improvement of the output voltage waveform quality of the modularized current transformer with the mixed sub modules is facilitated.