Cavity ring-down spectroscopy is a new type of high sensitive spectroscopy emerging in recent years. It can be subdivided into straight cavity, folding cavity and ring cavity ring-down spectroscopy by the structure of the optical resonator. In folded cavity ring-down spectrometer, the folded mirror surface may be polluted for various reasons. Different from straight cavity mirror, ring cavity mirror and folded cavity end mirror, there are two symmetrical beams incidence on the surface of folded mirror. So the performance of folded cavity in this case appears new characteristics, the most concerned one is that the scattering fields will produce an interference effect when two beams irradiate on the particulate. Embarking from the scattering theory and combining with the analysis of the light field in the resonator, this paper qualitatively analyzes the influence of the particulate loss on the performance of folded cavity ring-down spectrometer. These works have a guiding significance for the study of folded cavity ring-down spectroscopy and can improve its system performance.