High-dehydration hardenable plugging sealing agent

The invention relates to a high-dehydration hardenable plugging sealing agent which comprises the following components by mass percent: 35-50% of solidifying material, 25-35% of composite sealing agent, 5-15% of high-dehydration material, 5-10% of elastic expending material and 10-15% of fiber material, wherein the composite sealing agent is formed by mixing granular husk, mica and cotton seed hull in a mass ratio of 5:2:1; the solidifying material is formed by mixing gypsum, cement, blast furnace slag and sodium phosphate in a mass ratio of 1:1:0.5:0.1; the high-dehydration material is kieselguhr or coal ash; the elastic expending material is formed by mixing coated water-sucking rubber and coated water-sucking resin in a mass ratio of 1:1; and the fiber material is polyacrylonitrile fiber of 9-11mm. The sealing agent integrates with high dehydration, delay expanding, plugging solidification and physical overlap joint; and the formed sealing layer is not easy to destroy in the subsequent drilling process, thereby effectively improving the sealing efficiency.