Heavy metal ions in water or soil are serious pollution, and human health is seriously endangered by pollution. The removal of heavy metal ions quickly and efficiently has become an important research field. Chitosan is a natural high molecular polymer with excellent flocculation and metal chelation. The effect of pH values on the stability constant and chelation properties of chitosan chelated Cu2+ was studied by ultraviolet spectrophotometry in this work. The chelation performances of chitosan to copper ions were investigated with the pH value increasing from 1 to 9. The experimental results showed that the chelating ability of active groups on chitosan carbon chain with copper ion was enhanced with the increase of the pH value. When the pH values of the solution system ranged from 5 to 6, the stability constant of the chelate was the maximum value of 1.1×108, when the pH was close to 7, some chelate products precipitated and the stability constant decreased. The change of pH value had no obvious effect on the coordination ratio (n) of the chelate under acidic conditions and the ratio (n) was 2. The chitosan-Cu(II) chelate could be separated out by adjusting the pH value of the solution. With the increase of pH value, some floccules precipitated from the solution and the concentration of Cu2+ decreased. When the pH value was about 9, the Cu2+ concentration reached a minimum value of 1.5 mg/L. The precipitate of chitosan reacted with copper ions was analyzed by microscopic image, X-ray diffraction pattern and Fourier transform infrared spectroscopy (FT-IR), the results showed that the main component of the precipitate was chitosan-Cu(II) formed by chelation of –NH2 with Cu2+. This study could provide a theoretical basis for the removal of metal ions by chitosan.