One stalagmite (TK22-1) derived from the Tiankeng Cave in Youyang Autonomous County, Chongqing is used as the research object in this article. We established high-resolution and age-accurate grayscale sequence of the last 100 years with accurate ²³⁰Th dating, ²¹⁰Pb dating, and layer counting. We reconstructed the history of climate and environmental change of the last 100 years in Chongqing to make the significance of climate and environment that the stalagmite grayscale indicated more explicit by comparing with observed meteorological data. The results show that grayscale of stalagmite (TK22-1) is positively associated with the local mean annual temperature, while it is negatively associated with the local mean annual humidity and annual rainfall days. This indicates that climate conditions such as temperature and humidity are the main factors driving the grayscale to change. Karst trough valley area in the southeast of Chongqing is in the ecological environment fragile zone because the thin layer soil has weak storage capacity for precipitation. Water is one of the main causing leading soil humidity to change in this area. With high precipitation and high surface humidity, the retention time of rainwater in soil decreases and infiltration rate speeds up, eventually weakens the water-rock interaction and decreases the concentration of organic matter and impurities dissolved in the soilwater. Thus the purer calcite mineral crystallizes in the surface of stalagmite, and the grayscale decreases, and vice versa. With high temperature and high evaporation, the surface humidity and soil humidity decrease, which prolongs the retention time of water in soil and epikarst zone. The content of organic matter and CO₂ releasing from soil increases. Meanwhile, the concentration of organic matter and impurities in the cave drip water increases, resulting in the loose structure of calcite and more impurities in stalagmite, and the grayscale increases and vice versa. There is a good correspondence between drought events occurred during the past 100 years in karst trough valley area of the southeast of Chongqing and the stalagmite (TK22-1) grayscale sequence. The grayscale peaked when drought events happened. With the local precipitation decreasing, summer droughts occurred, and the grayscale increased, which indicated that soil humidity and water-rock interaction were the main factors affecting the stalagmite grayscale change.