The invention discloses high-temperature resistant high-strength alloy steel and a thermal treatment process thereof. The high-temperature resistant high-strength alloy steel comprises the following raw materials in percentage by weight: 0.02-0.05% of carbon, 3-6% of aluminum, 0.1-0.5% of thallium, 0.03-0.08% of rubidium, 0.1-0.4% of tin, 0.05-0.1% of niobium, 0.1-0.5% of lithium, 5-12% of titanium, 10-15% of gypsum whiskers, 10-18% of yttrium oxide, 6-11% of a tungsten carbide powder and the balance of iron. The high-temperature resistant high-strength alloy steel disclosed by the invention is prepared from carbon, aluminum, thallium, rubidium, tin, niobium, lithium, titanium, gypsum whiskers, yttrium oxide, the tungsten carbide powder and iron through five steps of thermal treatment processes, the obtained high-temperature resistant high-strength alloy steel has the advantages of being high in strength, high in temperature resistance, good in toughness, and the like, is long in service life and capable of well meeting production and use requirements, and in addition, a component made of the steel is not easy to break or deform, and is worthy of popularization.