Abstract: In order to predict more accurately the critical flow of fluidelastic instability, the motion equation of a cantilevered tube is established utilizing quasi-static fluid force coefficients of two-phase flow. After Galerkin discretization of the analytical model, the critical flow velocity of each void fraction is obtained by solving  the characteristic equations. Moreover the response of cantilevered tube is solved using Runge-Kutta algorithm. Numerical results show that the critical velocity of instability increases with the increasing of the void fraction, and the numerical results agree with experimental results, which proving the analytical model utilizing quasi-static fluid force coefficients of two-phase flow is available for predicting the critical velocity of fluidelastic instability.