Computational fluid dynamics (CFD) simulation technology can overcome the lack of traditional design methods in heat exchanger and gives a good means to improve the product quality. Created a digital model according to the structure of one engineering oil-water tubular heat exchanger, discretized the solving area with pre-processing software ICEM CFD to get the unstructured finite element grids, then solved the flow field by CFD software FLUENT, and attained the cloud charts of temperature, pressure and flow lines. The simulation result analysis implies that the numerical simulation method with CFD software for flow field is credible, which can be used as a useful complement to traditional methods, and also can be applied for optimization of the heat exchanger.