Abstract: In view of problems of complex structure of main circuit and limited power and voltage existed in traditional traction system of AC-DC-AC electric locomotive, a traction converter for electric locomotive with single-phase AC input and three-phase AC output was designed based on structure of modular multilevel converter using full bridge sub-module. The traction converter can drive traction motor directly, so as to eliminate vehicle-mounted step-down transformer and reduce complexity of traction system of electric locomotive. A constant AC voltage control strategy in outer loop and direct current control strategy in inner loop was proposed according to mathematic model of the converter established in two-phase synchronous rotating dq coordinate system. The simulation results verify validity of the converter and the control strategies.