The invention discloses a cooling unit for a traction system. The cooling unit for the traction system comprises a bearing and supporting framework, an air filtering device, a heat radiator, an air guide cylinder, a fan box body, an expansion water tank, a water pump and a fan unit as well as a water system pipeline, an oil system pipeline, pressure sensors, temperature sensors, a wire junction box and an electric rapid connector, wherein the water system pipeline and the oil system pipeline are communicated with the heat radiator; and the pressure sensors and the temperature sensors are arranged on the pipelines. An integral matched design method is adopted for the cooling unit provided by the invention; a cooling unit of a traction transformer and a cooling unit of a traction converter are integrated into the same unit, and at the premise of simultaneously meeting the heat radiation requirements of the traction transformer and the traction converter, the cooling unit for the traction system is small in size, light in weight, low in noise, compact in structure, high in reliability, convenient to install, and low in maintaining and repairing work load.