The invention provides a method for treating waste and sealing carbon dioxide of a pithead coal-fired power plant. The method comprises the following steps: mixing solid waste of the pithead coal-fired power plant with cement and a mixing liquid to obtain a filling, backfilling an exhaust coal mine with the filling, and carrying out densification; and injecting a hydration liquid into densified filling for hydration, injecting carbon dioxide waste gas of the pithead coal-fired power plant for well closing to mineralize carbon dioxide, so as to realize the sealing of carbon dioxide and the reinforcement of the exhaust coal mine. According to the method, by virtue of chemical reaction of rich alkaline oxide in the solid waste of pithead coal-fired power plant, calcium hydroxide and hydrated calcium silicate in hydrated cement and injected carbon dioxide, stable solid-state carbonate is generated, the sealing of carbon dioxide of the pithead coal-fired power plant, and the treatment of the solid waste and the reinforcement of exhaust coal mine are simultaneously realized. Calculation shows that by utilizing the method for treating the waste of the pithead coal-fired power plant, the sealing quantity of carbon dioxide can reach 406.2kg/m<3>; and an experimental result shows that the strength of an obtained simulated formation can reach 20MPa-30MPa.