Crosslinked carboxymethyl modified starch (CCMS) was prepared by chemical modification of nature cornstarch. This modified degradable polymer had turned out to be a strong ability to chelate heavy metal ions. Using the instrument of microwave plasma torch atomic emission spectrometer(MPT-AES), 20.00 mg/L of Cu, Zn, Ni, Pb, Cd were detected under the Sewage Discharge Standards requirements after adding 90, 154, 86, 70, 546mg/L of CCMS respectively. The separation of the heavy metal ions and CCMS solutions were used the technique of ultrafiltration, with a molecular weight cut-off (MWCO) of 50000. By the same treatment, the chelating sequence of the heavy metals were also measured and decreased in the order of Pb>Cu>Cd>Zn>Ni.