The invention relates to the field of 
phase change heat storage materials, in particular to a 
biochar-paraffin 
phase change heat storage material and a preparation method. The 
cut straw is heated to 800 DEG C + / - 20 DEG C in a tubular furnace filled with 
nitrogen at the speed of 1-3 DEG C / min and heat preservation is conducted for 1-3 h, so that the 
straw is cracked into a 
biochar material; and then the 
biochar material is placed in the hot 
air atmosphere of 400-600 DEG C to be subjected to 
surface oxidation treatment for 8-12 min; and the 
paraffin block is placed into a mold cavity of a moldwith addition of the biochar material subjected to 
surface oxidation, then the mold is heated to 70-90 DEG C with complete stirring to melt the 
paraffin block in the mold cavity, then the paraffin isuniformly mixed with the biochar material, and the product is naturally cooled and cured to obtain the 
phase change heat storage material. The biochar accounts for 10-20% by 
mass, and the paraffin accounts for 80-90% by 
mass. According to the biochar-paraffin phase change 
heat storage material, the 
heat transfer efficiency of the material is effectively improved, the 
volume change of the materialin the phase change process is stabilized, and the manufacturing cost of the material is reduced.