As a novel type of shell-and-tube heat exchanger，the fluid flow and heat transfer mechanism in flower baffle heat exchanger(FBHX) has not been studied deeply.In the present paper，the CFD simulation method is adopted to investigate the mechanism of fluid flow and heat transfer of FBHX.With the comparison of calculated results between heat exchangers with flower baffle and traditional segmental baffle respectively，it shows that the pressure drop of the former is only 45% of that of the latter，while the difference of heat transfer coefficient between the two exchangers are minor，therefore，the comprehensive performance of the former is 2.2 times of that of the latter.