The invention discloses a hyperbranched PEG (polyethylene glycol) crosslinking agent and an RAFT (reversible addition-fragmentation chain transfer) living radical polymerization method thereof. PEGDA(PEG diacrylate) is taken as a monomer, tetraethylthiuram disulfide is taken as a precursor of the RAFT reagent, AIBN (azodiisobutyronitrile) is taken as an initiator, PEGDA is initiated for RAFT living controllable radical polymerization, and accordingly, the PEG crosslinking agent with a hyperbranched structure is prepared. With the utilization of a one-pot reaction system, the preparation method is simple, the reaction conditions are mild, a prepared hyperbranched polymer has good water solubility and biocompatibility, has more branching point and contains many terminal functional groups, and an expected functional material can be obtained through modification of the hyperbranched polymer.