The invention provides a sub-module voltage equalizing method for a modularization multi-level current converter. The sub-module voltage equalizing method includes the steps that sub-modules are divided into a plurality of stages according to voltages and sequentially controlled, a sub-module voltage grading control method is adopted for dividing the sub-modules into m groups according to the voltages, when charging or discharging is needed, the sub-modules in the group with the maximum voltage value or the minimum voltage value are preferentially started, when the number of the sub-modules required to be started is insufficient, the sub-modules in the group with the slightly-small maximum voltage value or the slightly-large minimum voltage value are sequentially started to conduct charging and discharging, and the voltages of the sub-modules on a bridge arm are controlled within a scope; compared with a traditional voltage equalizing method based on a sort algorithm, time for complex sort calculation is saved, the control period is short, the control process is simple, and the sub-module voltage equalizing method meets the requirement of the modularization multi-level current converter for the continuously-increased level number.