The invention relates to a star-shaped polyglutamic acid as well as injectable hydrogel and a preparation method thereof. According to the preparation method, firstly, polyamino beta-cyclodextrin is stereospecifically synthesized, secondly, a plurality of polymerization reaction initiation sites are introduced so as to initiate ring-opening polymerization of L-glutamate-N-carboxylic acid anhydride, and finally the L-glutamate-N-carboxylic acid anhydride subjected to ring-opening polymerization is modified to be used as a first component of hydrogel; meanwhile, modified polysaccharide polymer is used as a second component of the hydrogel, the two components are mixed according to a certain ratio, through chemical crosslinking of the Schiff base reaction, the star-polyglutamic acid hydrogel is obtained, and the gelation time is 7-300 s. The hydrogel is characterized by having an excellent apparent appearance, mechanical properties, biocompatibility and biodegradability; in addition, beta-cyclodextrin is used as a core of the star-shaped polyglutamic acid, so that additional stable crosslinking sites are provided, the improvement of the mechanical strength of the hydrogel is facilitated, and the loading and controlled release properties to hydrophobic drugs are improved. The hydrogel has a wide application prospect in the fields of drug controlled release, tissue engineering, regenerative medicine and the like.