This paper describes in detail the experiment on the heat transmissibility of the radiator-water box ed in Shanghai santana automobile. Accolding to the real measurement data the coefficient of the convection heat-exchange of the outside row-arranged pipes is separated from the global heat transfer coefficient, and is processed into a dimensionless criterion. This gives a faithful refernce in optimum design. Further analysis on the inlet and outlet heat hansmissibility as Well as on the resistance force, confirm the resonableness of the heat tiansmissibilities index taken for the radiator-water box.