The invention relates to a modeling method and system of a diode clamped cascaded multi-level converter. All corresponding diodes of each bridge arm are equivalent to an auxiliary diode; all corresponding capacitors of each bridge arm are equivalent to a controlled voltage source; power modules of each bridge arm are connected in series to be equivalent to an equivalent module; and the equivalent module comprises a loss resistor and a composite equivalent model connected with the loss resistor. Since a plurality of components, at the same positions, in each power module of each bridge arm of the diode clamped cascaded multi-level converter are equivalent to a component, the node voltage equation order can be reduced, the simulation efficiency is improved, and the simulation efficiency cannot be reduced with the increase on the number of the power modules. By the modeling method and the modeling system for modeling, the demands for flexible DC power transmission engineering parameter design, control strategy verification and the like of a remote-distance, high-capacity overhead line occasion can be satisfied.