The invention discloses an energy-efficient and environment-friendly coal-fired boiler. Pre-combustion desulfurization and dehydration are conducted on coal based on the tail gas waste heat and microwave technology, and excess pure oxygen is used for supporting combustion in the combustion process of the coal in a combustor; by replacing air with excess pure oxygen, the total amount of combustion gas is reduced by 70-80%, and by means of excess pure oxygen combustion, the instantaneous effective combustion ratio of the fuel reaches the maximum limit value. Sulfur and nitrogen in the coal react with a desulfurization agent and a denitration agent in excess pure oxygen combustion to generate stable sulfate and nitrate, and then sulfate and nitrate are discharged along with slag, so that partial desulfurization and denitration are achieved. Liquid ammonia and ammonia water are sprayed to combustion tail gas with different temperatures to achieve complete desulphurization and denitration, and escaping ammonia is absorbed through an intelligent bubble-cap tower. The energy-efficient and environment-friendly coal-fired boiler has the advantages that the effective energy conversion ratio of the coal is increased by recycling tail gas energy, conducting microwave dehydration and desulfurization before combustion of the coal, recycling tail gas waste energy and conducting dehydration, the emission of hazardous substances such as nitrogen oxide, sulfide, sulfur oxide, carbon monoxide, benzene and long-carbon-chain macromolecular organic matter is reduced by means of excess pure oxygen combustion, and energy conservation and emission reduction are achieved.