The invention discloses a method for preparing a super-strong water-absorbing water-retaining agent, which comprises the following steps of: gelatinizing or dispersing a biomass base material which is easy to degrade to form a mixture of the gelatinized or dispersed biomass base material and an unsaturated graft monomer, regulating the pH value to be between 3 and 9, and adding a cross-linking agent; and adding an active material with bacteriostatic and antibacterial activity to initiate polymerization so as to prepare the super-strong water-absorbing water-retaining agent which has bacteriostatic and antibacterial effects and is easy to degrade. The super-strong water-absorbing water-retaining agent which is prepared from the biomass base material such as starch, cellulose, polysaccharide, protein and the like and is easy to degrade has high bacteriostatic and antibacterial characteristics, the problems of poor mildew prevention, water absorption and retention functions and persistent characteristics and the like of the super-strong water-absorbing water-retaining agent product are solved, the preparation process is simplified, reaction time is shortened, production cost is greatly reduced through water and energy conservation, and waste liquid is not generated in the process.