Abstract: The paper analyzed influence of dead time on single sub-module of modular multilevel converter and reached conclusions that the sub-module will produce positive dead voltage from inserted state to cut-off state when arm current is positive and negative dead voltage from cut-off state to inserted state when arm current is negative. It analyzed influence of dead time on ideal fundamental voltage of modular multilevel converter, and deduced formulas of equivalent amplitude of output fundamental wave of dead voltage, actual amplitude of fundamental wave and offset of angle of output voltage, so as to reach conclusions that when voltage of DC side is fixed value, influence of dead time on modular multilevel converter relates to carrier wave ratio, dead time and phase-difference between output voltage and output current and unrelates to numbers of input module, improving modulation depth of voltage and reducing dead time can reduce influence of dead time on modular multilevel converter effectively. Simulation result validates effectiveness of the above conclusions.