In order to establish the relationship between the charged characteristics of polysaccharides and protein complex systems， in this paper， the composite mechanism and rheology of CS and casein were characterized by fluorescence spectroscopy， ultraviolet-visible absorption spectroscopy， Fourier infrared absorption spectroscopy and rheological viscosity analysis. The results showed that the quenching of casein by CS was static in the fluorescence spectrum. At 303 K and 313 K， the binding sites of high deacetylation chitosan （HDCS） were 1.29 and 1.36， the number of binding sites for low deacetylation chitosan （LDCS） were 1.47 and 1.44， respectively. At pH 6.0， the interaction between HDCS-casein was mainly attributed to electrostatic interaction， LDCS-casein mainly ascribed to hydrophobic interaction. In the UV-visible absorption spectrum， the addition of LDCS did not change the microenvironment of tyrosine （Tyr） in casein. However， the addition of HDCS changed the microenvironment of Tyr in casein， increasing its polarity and stretching the polypeptide chain. Fourier transform infrared spectroscopy showed that the -NH3+ group in CS interacted with the -COO- group in casein. In the rheological steady-state viscosity analysis， the viscosity of the CS-casein complex solution increased with the increase of CS deacetylation degree.