Recently, most of research at home and abroad focuses on the analysis of transformer thermal problems, but there is little research about optimum design of plate-type radiator. From the perspective of heat transfer and fluid mechanics, theoretical analysis and simulation calculation were used to transform the plate-type radiator structure. It can be seen from the results that the oil duct optimum angle is 13 degrees similar to 20 degrees, at the same time the big oil duct is divided into three small oil ducts; the heat transfer efficiency is higher. When the side oil duct is designed into wide one and the middle duct is designed into narrow oil duct, it will obtain well heat transfer effect.