The work aims to realize the composite application of alginate/chitosan by studying the effect of alginate/chitosan loading on the paper and the isothermal absorption property of the prepared composite paper for the pigment and metal ion. The cellulose filter paper was immersed and dried by anionic polysaccharide alginate and cationic polysaccharide chitosan quaternary ammonium salt in order. Compared with the filter paper base, the tensile strength and bursting strength were increased by 119% and 105%, respectively. Fourier transform infrared spectroscopy (FTIR) detection showed that the adsorption peaks of hydrogen bonds were broader and higher in composite paper, indicating an increased hydrogen bonding force. The adsorption isotherm fitting indicated that, the prepared composite paper showed good absorption properties for methyl orange, and its adsorption to Cu2+ conformed to Langmuir and Freundlich model equations, belonging to a monolayer adsorption. It is concluded that alginate/chitosan can be used to prepare mechanically enhanced composite paper with certain adsorption performance.