In this paper, on the basis of great test data, the heat exchange characteristics of the water cooling and radiating system for the Star-Steyr WD615 diesel engine series are analyzed in detail. From the characteristic of heat releasing of engine and the measured discharge curves of water pump and fan, the coefficient K of heat transfer and the radiating capability for the radiator of Model WD615.67 diesel engine are exactly computed. The computing results are conformable with the practical inspection of the diesel engine. The calculation of the radiator indicates that its heat transfer resistance comes mostly from the resistance of the water tube and the cooling rib to air. Therefore in the view of authors, the key to improve the heat radiating capability of a radiator is to decrease the heat transfer resistance of the radiator on the air side. Star-Steyr WD615 diesel engine series can meet the different requirements of beat radiating capability of the radiators by varying in size and rotative speed of the fan. The calculation also indicates that the water cooling and radiating system for Model WD615.67 diesel engine can allow itself to operate continuously under 35°C ambient temperature. Based on calculations and analyses, anthors make proposals for improving the water cooling and radiating system.