The invention discloses a technique for producing water-soluble functional chitosan. The technique comprises the steps that: chitosan is added into H2O2, and the mixture is mixed evenly, microwave-heated for a proper time, and is cooled; the chitosan treated by microwave is added into the solutions of acetic acid or hydurochloric, and is stirred until the chitosan is fully dissolved; chitosan solution is prepared after pH is adjusted to 5 to 6; non-specific chitosanase is added into the chitosan solution, and zymohydrolysis, enzyme-annihilation, enzymolysis liquid filtering and centrifugalization are carried out to remove precipitate, and then a clear solution is obtained; hyperfiltration is carried out on the clear solution, and nanofiltration is carried out to the hyperfiltrated solutionto remove salinity and micromolecule monosaccharide; filtrate is sprayed and dried, and then the product is obtained. The technique organically integrates microwave degradation, oxidative degradationand zymohydrolysis and adopts non-specific enzyme to solve ab enzyme preparation supply problem; the controlling parameters of zymohydrolysis is comparatively moderate; the technique is applicable tothe scale production of water soluble functional chitosan.