High efficiency and high power density are becoming increasingly popular in the design requirements of power electronic converters. In thispaper, the design and optimization method of a three-phase T-type converter are discussed. Loss models of the converter are formulated by theconventional method. The switching frequency, peak flux density, number of turns, number of layers,..., are optimized using genetic algorithmfor minimizing the overall converter loss. Simulation results prove that the loss models are reliable. The optimized converter has improvedperformance with a high efficiency of up to 99.47% and a low-temperature rise of fewer than 50 degrees Celsius on both inductors andsemiconductor devices. The utilization of computer-aided design methods also significantly contributes to reducing the workload of designers.