Abstract: A new procedure is proposed to derive the analytical fragility models of simply supported highway bridges based on an improved response-surface method. By considering of the uncertainties in the structural and material properties of the bridges, the bridge samples were obtained by Plackett-Burman design method. From the nonlinear time history analysis through the OpenSees software, several parameters that affect the seismic response of the bridge significantly were identified. From the bridge samples obtained by using the central composite design (CCD) method with the chosen optimal parameters focused on, response surface models under different PGA levels were established from the finite element models with respect to each component's response. The simply supported bridge system was assumed to be a series system and the fragility curve was obtained by Monte Carlo simulation method. From the same bridge samples, fragility curves generated by means of incremental dynamic analysis were used as a benchmark. The results of the traditional response surface method and the improved response surface method were compared to each other. It is found that the improved response surface function could efficiently replace the complex nonlinear time history analysis and improve the efficiency of the fragility analysis. These resulting fragility curves will assist the users to identify the vulnerable bridge components over a large seismic intensity range and aid the bridge management decision-making process to prioritize the seismic strengthening repairs. Therefore, it is comparatively valuable as a new procedure in relevant civil engineering applications.