This article reviews the thermal design of motors, including the relationship between the maximum temperature of windings and the motor life span, the relationship between the heat source of the motor at different speeds and the type of the motor in the thermal design. Through some literature survey, a complete thermal management overview is provided. In addition, the advantages and disadvantages of thermal systems used in common enclosed motor are analyzed among each other. Finally, some typical case studies concerning the temperature distribution are presented and discussed. The summarized results are useful in designing motors and can be used to improve the motor operating efficiency and life span, and minimize the cost of manufacturing and maintenance.