A multi-functionally modified polymer binder for lithium ion batteries, which is prepared by a free radical graft copolymerization or a Michael addition reaction, with a biomass polymer or a synthetic polymer as a substrate, and a hydrophilic monomer and a lipophilic monomer as functionally modifying monomers. The binder presents a three-dimensional network body with a multi-branch structure, provides more active cites for contacting with the electrode active materials, improves uniformity and flatness in the formation of films from electrode slurry, enhances the binding strength between the electrode active materials, the conductive agents and the current collector, has high elasticity and binding strength, and is applicable in water/organic solvent. Use of the binder in positive electrodes and negative electrodes can facilitate the conduction of electrons/ions during charging and discharging, reduce the electrochemical interface impedance of the electrodes.