The invention relates to the crop growing field, particularly relates to a soil improver taking biomass particle carbide discarded in agriculture and forestry as a matrix and a preparation method thereof. The carbon-base soil improver comprises biomass particle charcoal, calcium magnesium phosphate or calcined lime, and binder, and also comprises other fertilizers, such as urea, monoammonium phosphate powder, potassium chloride, zinc sulfate, boricfertilizer, manganese sulfate, ammonium molybdate, ferrous sulfate and copper sulfate and the like. The biomass particle charcoal is a black powdered carbon particle (carbon soot) generated by incomplete combustion of the biomass under hypoxemia condition, has various properties similar with soil humus (acid) and strong ability to absorb and maintain nutrients, such as nitrogen, phosphorus and potassium and the like, and has obvious water retention and moisture preservation effects. The soil improver prepared by the preparation method has the characteristics of soil structure improvement, moisture and fertility preservation, temperature increasing, efficient environmental protection and wide application prospects and the like.