The effects of different water content on the high molecular polymers in cefodizime sodium were investigated by gel filtration chromatography. In the column(Sephadex G-10),the mobile phase A was phosphate buffer solution with 0.02 mol·L^-1（pH=7.0）and the mobile phase B was ultrapure water,the flow rate was 1.0 mL·min^-1,and the detection wavelength was 254 nm. It was a good linear relation in range of 10.536～34.461 mg·mL^-1 (r = 0.998 6) between the peak area ratio of high molecular polymers vs internal standard and its concentration. The content of polymer was increased significantly with the increase of water content in cefodizime sodium. It was founded that water was the key factor to control the concent of the high molecular polymers in cefodizime sodium.