The invention discloses a method for increasing the fixed carbon content of medium-and-low-rank coal. The method includes the following steps that firstly, medium-and-low-rank coal raw ore is smashed, ground and screened to obtain small-granularity raw pulverized coal; secondly, the small-granularity raw pulverized coal is subjected to high-pressure alkaline leaching; thirdly, the small-granularity raw pulverized coal subjected to high-pressure alkaline leaching is filtered and washed; fourthly, the washed small-granularity raw pulverized coal is dried. The method has the advantages that the high-pressure alkaline leaching is adopted, the medium-and-low-rank coal is soaked in a low-concentration alkaline solution in the high-pressure environment, ash content in the coal is dissolved in alkaline liquid, carbon is not soluble in the alkaline liquid, filtering is conducted after alkaline leaching, the ash content dissolved in the alkaline liquid is separated from carbon in the coal, accordingly the carbon content of the medium-and-low-rank coal is effectively increased, the whole treatment process is not involved with high-temperature reaction, and high-concentration alkaline liquid is not used; therefore, energy consumption is low, and cost is easily controlled.