The aim of this paper is to study the nonlinear stability and dynamics behaviors of a simplified partially-filled satellite．The sufficient condition of stability of the satellite was obtained using Lyapunov direct method．Also we point out the critical parameter when Hopf bifurcation occurred and determine stability of Hopf bifurcation．At last，By the track in the phase space and the largest Lyapunov exponent，the nonlinear mechanisms in system are analyzed．