A comparative study on performances of rod-baffle (RB) and segment-baffle (SB) heat exchangers was carried out by numerical simulations under the same conditions. The results show that the overall heat transfer efficiencies are similar in these two types of heat exchangers with the same heat transfer areas. But RB heat exchangers show more uniform and smooth fluid flow, as well as much lower pressure in the shell side compared to SB counterparts. These detailed characteristics of heat transfer and fluid flow evidence better performances in RB heat exchangers and also provide a deeper insight into design and optimization of shell-and-tube heat exchangers.