The invention discloses a quick estimation algorithm for the valve loss of a modularized multi-level current converter, and the algorithm comprises the steps: 1, building a MMC rapid simulation model according to system parameters and a control method; 2, enabling a submodule capacitor voltage, a switching device trigger pulse and a bridge arm current in the simulation results to be stored as a readable data file; 3, building a mathematic model for switching device loss calculation and PN junction temperature estimation according to the characteristic parameters of a switching device in an MMC submodule; 4, enabling the data file to be imported into a loss calculation program, and calculating the valve loss of a single IGBT and a diode at each data step; 5, carrying out superposition to obtain the valve loss power of the MMC through iterative computation according to the relation between the valve loss power of the IGBT and the diode and the junction temperature. The method solves a problem that the voltage and current of the MMC submodule and the working temperature of a converter valve cannot be calculated precisely through analysis, and can be widely used for the technical field of flexible DC power transmission.