Abstract: he LS13320 laser diffraction particle size analyzer is used to analyze the grain size of speleothem in Jinyuandong. The measured data are generated to grain size frequency curves by the Grapher software to calculate the parameters for the study of grain-size characteristics and sedimentary environment of the Pleistocene red cave deposits. The results show that the silt content dominates the size composition, with average value of 50.14%, among which the fine silt is more than coarse silt, followed by clay content, and the sand content is the least. The grain size frequency curves of sediment samples demonstrate multimodal. Based on the calculation of particle size parameters, it is inferred that the sedimentary environment is dominated by wind deposition, which is then transported by running water, yet the compositions of sediments haven't changed significantly, reflecting the weak hydrodynamic force. The material sources are mainly influenced by climate, mostly proximal deposit in dry-cold and far-source deposit in warm-humid environments.