The invention belongs to the field of nonferrous metallurgy, in particular to a method for preparing vanadium trioxide through bone coal vanadium extracting vanadium-rich liquid. The method includes the following steps of firstly, conducting pH adjustment on the bone coal vanadium extracting vanadium-rich liquid with vanadium concentration larger than 6 g/L by means of alkali liquor or acid liquor to obtain to-be-reduced liquid with hydrogen ion concentration of 10<-4>-10<-14> mol/L; secondly, conducting stirring reaction on hydrogen and the to-be-reduced liquid in a high-temperature high-pressure reaction device at temperature of 50-300 DEG C and hydrogen partial pressure larger than 1 MPa for 1 h or more to obtain vanadium trioxide water slurry; thirdly, conducting solid-liquid separation on the vanadium trioxide water slurry to obtain a vanadium trioxide filter cake and filtrate; fourthly, conducting vacuum drying on the vanadium trioxide filter cake to obtain vanadium trioxide. The method has the advantages of being simple in process, friendly to the environment and low in production cost.