Abstract: Based on force balance method, the nonlinear differential equation of heat transfer tube, subjected to internal and external flows together with loose support, was developed. The nonlinearity associated with the mean axial extension of the tube was accounted for in the current work. Meanwhile, the interaction of tube vibration and fluid force induced by cross flow were modeled by wake oscillator model. The response of the coupling system was calculated using a fourth order Runge-Kutta integration algorithm and the nonlinear dynamics characteristics were studied. The bifurcation diagrams for vibration amplitude with cross flow velocities were constructed. The results show that the internal flow velocity has remarkable effect on coupling system of heat transfer tube with loose support.