The invention provides multi-tooth bionic ligand for improving biocompatibility and stability of nano particles as well as a preparation method of the multi-tooth bionic ligand. The synthesis bionic ligand is formed by coupling hydroxyl or carboxyl terminated mono-capped alkoxy polyethylene glycol and a carboxylic group of a carboxylic acid compound with a catechol group with an amino group of chitooligosaccharide. Due to the fact that three different kinds of interface action force including coordinate bond of the catechol group and metal, wrapping of the nano particles by micelle formed by a zwitterionic structure and electrostatic attraction between positive charges of the ligand and the nano particles exist between the bionic ligand and nano particles, accordingly, self-assembly modification is performed on the surfaces of the nano particles through triggering of different kinds of interface action force, compact protection films are prepared on the surfaces of the particles, the nano particles can be transferred into a water phase, and the nano particles with good dispersion and stability are obtained. The water-soluble nanometer particles obtained with the method can be applied to the bioimaging field such as MRI (magnetic resonance imaging) contrast agents and the like.