Stochastic resonance is a kind of nonlinear phenomenon, which can enhance the weak input signal through the nonlinear system. This paper investigated the phenomenon of stochastic resonance for duffing oscillator. Following experiments were studied: the relation between the output SNR with the noise strength, the relation between the output SNR of the Duffing system with the frequency of the sine signal, and the relation between the output SNR with the damping ratio. The experimental results show that the damping ratio parameter has an important role in the stochastic resonance and there exist a complex nonlinear relationship between the damping ratio parameter with the output SNR.