Chemical treatment, UV-light and filtration are water-supply’s disinfection method of microbe. UV-Disinfection has emerged as the best available technology of water treatments for inactivation of microbe. UV-light provides reliablity for microbe inactivation, whitout the formation of disinfection byproduct. however design of UV-Reactor is very difficult due to high-cost of test facilities and uncertainty. Therefore CFD tool become a mainstay for the design precess of UV-Reactors. For the reduction of experimental cost, particle in CFD assume to MS2 Phage that microbiologic for study. Thus analyzed about Particle Tracking method influence to Reduction Equivalent Dose.