The invention belongs to the technical field of a lithium ion battery and particularly relates to a preparation method of a lithium ion battery negative electrode material. The method comprises stepsof in the inert gas atmosphere, mixing tin precursor with organic solvent, adding surfactant, heating to 200-215 DEG C, adding reducing agent, and reacting for 5-10 minutes; then adding antimony precursor to react for 5-7 minutes to form a tin-antimony nanocrystalline alloy crude product; and lastly, obtaining the tin-antimony nanocrystalline alloy negative electrode material with the uniform particle size through short-chain ligand replacement. The method is advantaged in that the tin-antimony nanocrystalline alloy negative electrode material with the uniform particle size prepared is used asa bimetallic alloy material, as alloying reaction potentials of tin and antimony with lithium ions are different, the volume change of the negative electrode material and damage of stress generated in the material to the material structure in the charging and discharging process can be effectively inhibited, so stability of the material structure is maintained, cycling stability and safety performance of the lithium ion battery are effectively improved, and the lithium ion battery has high theoretical capacity.