As a type of the ship stability failure modes, parametric rolling has attracted more attention from many researchers in recent years because of a series of accidents due to ship instability, especially the instability of container ship. Parametric rolling is a complex nonlinear stochastic dynamic problem, which is often accompanied by large amplitude vertical motions of ships. At present, there are many difficulties in the research of ship parameter rolling, mainly including the nonlinearity of parameter rolling motion, the random variation of wetted area of the hull surface up to the incident wave waterline and the coupling effect of rolling, pitching and heaving. Nowadays, the potential flow theory is a common method to predict parametric rolling, but this method may generate results with low accuracy in some conditions. This paper describes a numerical simulation method based on in-house CFD code HUST-Ship to analyze parametric rolling motion of KCS (KRISO Container Ship) container ship model. The paper studies the occurring conditions of parametric rolling motion of KCS model and reveals the mechanism of parametric rolling.