The invention discloses a biomass solid clean fuel as well as a preparation method and application thereof. A percentage of carbon atoms in the biomass solid clean fuel is 37.15%-50.24%, and the highcalorific value is 13.50 MJ / kg-22.22 MJ / kg; and the clean fuel is prepared by the following steps: sludge and biomass waste are used as raw materials, pre-treatment is performed, acid-base treatment is performed, hydrothermal carbonization treatment is performed, hot press molding is performed, and therefore the clean fuel is prepared. The biomass solid clean fuel disclosed by the invention has the advantages of a high carbon content, a low nitrogen content, a high calorific value, less pollution, simple and easy preparation and low costs, and is a novel clean material; the preparation methodhas the advantages of a simple and easy preparation process, low costs, less energy consumption, short consumed time and conditions easy to control; and the biomass solid clean fuel has the advantagesof simple operation, high energy conversion efficiency and less secondary pollution when being used for combustion to generate energy as a fuel, and the energy clean utilization of the biomass solidclean fuel can be realized.