Dental plaque biofilm is one of the main factors that induce oral diseases. Due to the continuous fluidity of saliva and poor permeability of drug in the biofilm, the effect of traditional oral antibacterial agents is limited. In this work, nanogel CSN has been prepared via the physical crosslinking of carboxymethyl starch (CMS) and stannous ion (Sn2+), of which the adhesion to caries-induced Streptococcus mutans (S. mutans) biofilm was enhanced by further complexing chitosan (CS). Structure and morphology of all above materials have been characterized by 1H-NMR, FT-IR, Zeta potential and TEM measurements. As a novel drug delivery system, CS/CSN@MH was finally formed by encapsulating minocycline (MH) in the gel, while the drug encapsulation efficiency and loading rate was estimated as 76.48% and 10.64%, respectively. Different from the sudden release effect of free MH in simulated oral environment, the cumulative release of CS/CSN@MH within 48 h was 47.46%. The residual S. mutans biofilm after CS/CSN@MH treatment was only 13.76%. The removal of biofilm was also confirmed by live/dead bacterial staining assay and bacterial morphology after treatment.