Since 2002, 17 sinkholes have occurred in the karst valley of Hanpoao village-Baishiling village in Xinhua County, Hunan province, China, resulting in 58 collapse pits. The sinkhole is still occurring. In order to find out the formation mechanism, extensive investigations including field investigation, geophysical prospecting, exploratory boreholes, real-time monitoring of karst water pressure and rainfall and geotechnical test of soil samples were carried out. The results show that the karst valley of HanPoAo village -BaiShiLing village is located in the dry area of coal mine drainage, and the sinkholes are induced by the joint influence of human factors (coal mine drainage) and natural factors (rainfall). The human factor changes the groundwater recharge condition, causes the groundwater recharge to be insufficient, the groundwater level decreases, and exacerbates the groundwater activity in the collapse area. Natural factors on the one hand accelerate the seepage erosion effect, on the other hand, cause the groundwater level to rise sharply, the karst pipeline to produce upward pressure, resulting in air explosion effect. After the water level is dry, the formation process of the sinkholes of the karst valley is as follows: The rainfall causes the Quaternary soil to be saturated, the water level rises to cause the air explosion, the gas explosion destroys the soil structure near the bedrock surface, and the karst soil hole is formed near the bedrock surface. Under the influence of the effect of air explosion and the seepage erosion of rainfall, the roof of soil cavern collapses continuously and develops to the ground, and finally forms a collapse pit on the surface.