In micro space, mixing and heat transfer are promoted by changing the balance of transport properties. Mixing in micro space is categorized into two types: rapid mixing and precise diffusion control. In this paper, these mixing types were expressed in terms of micro fluid segment. Since rapid mixing is accomplished through proper design of the micro mixer, the logic of micro mixing was summarized with the effect for the production of nano-particles. The possibility of a new reaction system design was also evaluated by the effectiveness for a strict control of active species based on the reaction mechanism. On the other hand, it was shown that precise diffusion control by designing a micro space had a significant effect for strict control of nano-particle size. In addition, the layout of micro fluid segments in the microreactor was also effective for controlling the selectivity of multiple reactions. Based on these results, a method of reactor design including segment shape was proposed as a vector of new reaction engineering for process intensification.