The vortex-induced vibration of a single and a pair of equal-sized circular cylinder separated by 5.5D in tandem arrangement is investigated. The computations are carried out for various values of reduced velocity of the oscillator (Ur=1.85~9.7). The results of numerical simulation for a single cylinder by the present method are observed close to the data of experiment. And then, the dynamic response and force coeeficient of two cylinders can be achived by the same method. The results show that the upstream cylinder responds qualitatively similarly to a single cylinder. While the downstream cylinder shows a different behavior. All kinds of cylinders undergo a figure of 8 motion.