The chelating ability of chitosan derivative 6-carboxy-chitooligosaccharide (CCOS) to calcium ions was studied, and the preparation technology of 6-carboxyl chitosan chelated calcium (CCOS-Ca (Ⅱ)) was established, to provide new ideas for the development of chitooligosaccharide-based metal complexes and high-performance calcium supplement. Chitooligosaccharides (COS) was used as experimental materials to prepare CCOS by oxidation of hydroxymethyl groups at the C6 position of chitooligosaccharides into carboxyl groups by TEMPO oxidation. Using CaCl2 as the calcium source, through the discussion of pH value, reaction temperature, reaction time, CCOS and CaCl2 mass ratio on CCOS-Ca (II) rate were studied, using three factors and five levels central composite rotatable design to optimize the preparation process. The products were analyzed by Fourier transform infrared spectrum scanning (FT-IR) and elemental analysis (EA). Regression analysis of response surface test data was carried out by using Design-Expert software. The optimum process parameters for CCOS-Ca (Ⅱ) preparation were as follows: the pH value was 8.3, the reaction time was 60min, the reaction temperature was 50℃, and the mass ratio of CCOS to CaCl2 was 34. Under the optimized conditions, the chelating rate was 88.86%. The structure of CCOS-Ca (Ⅱ) complex was confirmed by IR and EA analysis, and the molar ratio of CCOS to Ca2+ was 2∶1. The CCOS molecule contained —OH, —NH2 and —COOH, which can effectively chelate calcium. The effect of pH value, reaction temperature and ligand mass ratio on the chelation results was significant. CCOS-Ca (Ⅱ) complex can not only play the unique biological activity of chitooligosaccharides, but also may play a synergistic effect, enhance both the chitooligosaccharides and Ca2+ biological activity, and it was expected to prepare new calcium supplements.