The Micro-Whirling Coagulation process whose core is the Micro-whirling reactor is the key to the Whirling Clarification technique. The Micro-whirling reactor and its working mechanism which is whirling-coagulation and contact-flocculation are illustrated in this paper. Also it tells us the application on clarification tank in one wastewater reuse plant of BAOSTEEL. After being alteration to the standard clarification tank which is put the Micro-whirling reactor into the first and second flocculation area and put the inclined pipes into the sedimentation area, the treatment scale of the whirling clarification tank is increased, the effluent turbidity of the tank is lower than 3 NTU, the effluent turbidity of finished water is lower than 1 NTU and the investment of per ton micro-whirling water is lower 35 yuan RMB. The paper argues that in comparison to other coagulation reactors, Micro-whirling reactor deserves widely application for its various advantages, such as its higher coagulation efficiency, shorter reactivity time, better quality of finished water, stronger adaptive capability, more conveniences in construction and the like.