Abstract: For shell-and-tube oil cooler with water cooling, the heat transfer resistance on the shell side is 80% of the total heat transfer resistance of the cooler,so oil heat transfer resistance is controlling.It is a key factor to increase heat transfer coefficient of oil on the shell side for making high performance oil cooler.Two measures to be taken to increase heat transfer coefficient of oil,are first to use highly effective enhanced tube,and second to use novel shell side baffle geometry.Petal-shaped fin tube has special three-dimensional fin, it can effectively induce turbulence of oil flow,help to form a thinner oil boundary layer.Helical baffle produces a psuedo helical flow path on the shell side.It is shown experimentally that when turbulent flow is guided through a tube bundle of a certain helical angle, significant enhancement of shell side coefficient is achieved. In this paper,the heat transfer and pressure drop performance of petal-shaped fin tube oil-cooler with helical baffle is compared with that of low fin tube oil-cooler with helical baffle.The experimental results show that the total heat transfer coefficient of petal-shaped fin tube oil-cooler with helical baffle is 10% higher than that of low fin tube oil-cooler with helical baffle,and pressure drop is 46% lower than that of low fin tube oil-cooler with helical baffle.