The invention provides a method for preparing a lithium ion battery negative electrode binder, and a method for preparing a lithium ion battery negative electrode material. The crosslinked PEI binderprepared in the invention has the advantages of high solubility in water, low toxicity, non-flammability, greenness, environmental protection, and realization of industrial production; the prepared crosslinked PEI binder has a hyperbranched network structure, and the structure can form a multidimensional strong hydrogen bond together with silicon in order to firmly wrap silicon nano-particles, andthe flexible hyperbranched PEI molecular chain can effectively buffer the stress generated by the volume expansion of silicon, and flows to the damaged surface when the volume of the silicon shrinksto afresh form a hydrogen bond in order to achieve an effective self-repairing effect; and the network structure can effectively limit the movement of silicon, improve the deformation resistance of electrodes and ensure the integrity of a negative electrode, and can effectively solve the volume effect of the silicon negative electrode, so the cycle stability of the silicon negative electrode is greatly improved, thereby the demand of electric vehicles and other large energy storage devices for high specific capacity batteries is met, and the development prospect is broad.