The stochastic resonance of cascaded bistable Duffing system (CBDS) has been studied in this paper. We have shown that with the appropriate adjustment of the parameters of the CBDS, such as the scale transformation coefficient, the damping ratio and the number of cascaded systems, the CBDS can not only achieve large or small parameter stochastic resonance, but also optimize the stochastic resonance result of a single bistable Duffing system (SBDS). That is, with the parameter adjustment, the stochastic resonance effect of the CBDS is much better than that of the SBDS. Furthermore, the CBDS has excellent filtering and smoothing characters for a square wave signal, which can be applied to the recovery of the square wave signal masked by heavy noise.