In order to quicken the pace of the frequency selective surface (FSS) design and optimization, an equivalent circuit method is used to analyze the miniaturized-element FSS structure loaded with lumped elements. According to the physical structure of the FSS, an equivalent circuit model is established. These parameters values of the equivalent circuit model are obtained by a curve-fitting process using ADS to obtain the best fitting between the circuit response and the full-wave analysis response. The fitting accuracy is improved by increasing the curve frequency and the extrema. By using the circuit model, the frequency responses of the FSS at different LC values of lumped components are obtained. The transmissions at center frequencies calculated by the circuit model are slight higher than the exact results from the full-wave analysis, and the relative errors between the center frequencies and the –3 dB bandwidths are smaller than 10%. This paper proves that it is feasible to analyze the complex FSS structure by the equivalent circuit model based on curve-fitting process. It will give some references to the quick design and optimization of the FSS.