Abstract: The vortex-induced vibration of two cylinders with the effect of the stagger angle is studied numerically. A finite difference model based on an in-house code named CIP (constraint interpolation profile) is utilized. The model is built on a Cartesian coordinate system, with the Navier-Stokes equation solved by a third-order accuracy CIP method. The fluid-structure interaction is modelled by an immersed boundary method. Based on the CIP model, two-dimensional flow past two equal-sized circular cylinders placed at Reynolds number ( $\mathit{Re}=100$ ) with different stagger angle ( $\alpha =0^{°}\mathbf{~}90^{°}$ with a 15 #x00B0; interval) is investigated. Main attention has been paid to the lift coefficient, drag coefficient, displacement response, vortex-shedding frequency and wake pattern of both cylinders. The results show that the drag coefficient and lift coefficient of both cylinders increase monotonically as the stagger angle increases when reduced velocity $U_r=2.0\mathbf{~}3.0$ . For reduced velocity $U_r=5.0\mathbf{~}8.0$ , with the increase of stagger angle, the drag coefficient of both cylinders changes slightly and the lift coefficient of both cylinders presents a “convex-like” trend and reaches maximum value at $\alpha =15^{°}\mathbf{~}30^{°}$ . In the case of reduced velocity $U_r=10.0\mathbf{~}13.0$ , with the increase of stagger angle, the drag coefficient of both cylinders also displays little change and the lift coefficients of both cylinders show a “concave-like” trend and reach minimum value at $\alpha =30^{°}\mathbf{~}45^{°}$ . However, there is no obvious correspondence between the transverse oscillation amplitude and lift coefficient of cylinder as $U_r=10.0\mathbf{~}13.0$ . Finally, the wake pattern of both cylinders is analyzed to explain above phenomenon. Above all, the present result could be helpful to the structure design of ocean engineering.