Abstract: In this paper, A CIP-ZJU (Constrained Interpolation Profile method in Zhejiang University) model is developed to study a forced oscillating circular cylinder at low KC (Keulegan-Carpenter) in static fluid and flow past an in-line forced oscillating circular at Reynolds number of 200. The model was established in the Cartesian coordinate system, using the CIP method as the base flow solver to discretise the Navier-Stokes equations. The fluid-structure interaction is treated as a multiphase flow with liquid and solid phases solved simultaneously. An Immersed boundary method was used to deal with the boundary of solid body. Computations were compared with available results and good agreements were obtained, validating the reliability of the method to solve the problems of complex flow.