This paper presents a three dimensional simulation of the vortex induced vibrations of three elastic cylinders in regular triangle arrangement at high Reynolds number. The motion of every single cylinder, which is free to oscillate in two degrees of freedom in a uniform flow and has the same mass and natural frequency in both X and Y directions, is modeled by a mass spring damping system. The displacement and lift forces for each cylinder are analyzed with five spacing ratios L/D changing from 2.5 to 6.5. The results indicate that the downstream cylinders are usually undergone serious fluctuating lift forces. It is found that the simultaneous resonance in the X and Y directions may occur for the downstream cylinders. The stream wise oscillation of downstream cylinders could be as large as 0.54D, and the maximum transverse amplitude of three cylinders can reach to 2.30D. It is indicated that the cross flow oscillation amplitude of three cylinders significantly increased compared with the flow induced vibration of a single elastic cylinder and the stream wise oscillation of downstream cylinders is unneglectable for vortex induced vibration of multi cylinder system.