Abstract: In this paper, we study the Hopf bifurcations of the van der Pol-Duffing type nonlinear oscillator under the stochastic external influence and the internal parametric excitation. It is shown that the Hopf bifurcation point exhibited in the deterministic system is sensitive to the stochastic external influence and the parametric excitation. The addition of a small stochastic parametric excitation gives rise to a shift of the bifurcation point, which will be earlier than that of the ordinary system for a van ...