This paper is the result of environmental geological survey engineering. Objective The cascade of disasters caused by landslide–dammed lakes is highly destructive, with its formation and outburst processes significantly influenced by the external environment. The sediment within the dammed–lake serves as a valuable tool for documenting the entire lifecycle of thedammed–lake, offering important insights into paleoenvironment and paleoclimate. Utilizing the most effective analytical methods to interpret this sediment can aid in reconstructing the sediment deposition process and understanding changes in paleoenvironment. Methods Through sediment sampling for field investigation and laboratory analysis, the suitability of statistical characteristics of dammed lake sediments is assessed using graphical and moment methods. The sediment environment of the dammed lake is reconstructed by analyzing particle size in conjunction with organic matter content, allowing for the restoration of the development process of the dammed lake. Results (1) The stratified sediment sequence of the dammed lake sediment is distinct, representing a monogenic hydrodynamic lacustrine sediment with consistent material sources rather than polygenic sediment. Analysis of the organic matter and sediment grain size variations indicates that the dammed lake has undergone four cycles of wet–dry periods, with at least three instances of blockage–overflow deposition processes resulting from the combination of climatic and geological factors. The estimated sedimentary cycle period is approximately 1750 a. It is suggested that the sedimentation history is a consequence of prolonged and intricate activities within the fault zone, as well as the combined influence of climate and river dynamics. (2) The statistical analysis results from the graphical method and the moment method indicate a high level of agreement in assessing the average grain size and sorting coefficient, suggesting that they are interchangeable. However, the partial kurtosis values obtained from the moment method are greater than those from the graphical method, necessitating a linear adjustment for practical application. Additionally, deviations from statistical expressions are observed in the skewness and kurtosis due to the reference value description. Conclusions The grain size distribution of the sediment from the dammed lake is straightforward and easily calculated, making it convenient for comparison with other sediment types. The graphical method is suggested for these calculations. The findings indicate that the grain size characteristics offer valuable insights into understanding the deposition and outburst processes of dammed lake, as well as the response of landslide disasters to climate change. This information can serve as a theoretical foundation for reconstructing the paleoenvironment and paleoclimate of the dammed lake during its deposition phase.