Using CFD method, the flow field of oil-water tubular heat exchanger is calculated, and the heat transfer characteristic is analyzed. For the default of the heat flow field, the baffle technology is proposed to improve its structure design, and the conditions of heat flow field for the two structures are compared and analyzed. The results show that the two heat exchangers with different baffle structure can avoid excess temperature in some local region, and the heat exchanger with inside circle baffle has less on-way resistance, so it is considered as the optimal structure.