Abstract：Waste water with phenol is very harmful to the health of human beings. In order to effectively solve the serious problem of 2,4-dichlorophenol's pollution to water resources, the salicylaldehyde-modified chitosan's synthesis and its property of adsorption to 2,4-dichlorophenol are studied. A comparison of the adsorption ability between the modified chitosan and the un-modified chitosan is made. The synthesis method of salicylaldehyde-modified chitosan is discussed. The structure of the modified chitosan is characterized by FT-IR. The adsorption of 2,4-dichlorophenol by the modified chitosan is investigated by the UV spectrum method. The effects of pH value, time and concentration of phenol on adsorption property are analyzed. It is shown that the modified chitosan has better adsorption property than the un-modified chitosan. The adsorption ability is improved from 26.8mg/g of the un-modified chitosan to 38.7mg/g of the modified chitosan. The modified chitosan has the best adsorption effect when the adsorption time is above 2h and pH value of the solution is 5. With the increase of the concentration of phenol, the adsorption capacity is increased near linearly. After 50 minutes, the adsorption capacity of the modified chitosan approaches almost saturation. When the mass of the modified chitosan is above 0.5g, the adsorption capacity reaches the maximum. The adsorption property fits well with the Langmuir isotherm adsorption equation. The adsorption kinetics fits well with the second-order dynamic model.