Abstract: Yam starch was extracted through soak process by whitewash with yam powder which was from fresh yam as raw material.A standard curve was got based on the line relationship between absorption difference and content of starch,which the concentration cycle of standard amylose and amylopectin were used. This research had finally got 600 nm for measure wavelength while 560 nm for reference wavelength of amylase,532 nm for measure wavelength while 644 nm for reference wavelength of amylopectin according to the amylose and amylopectin complex full wavelength absorption spectra with iodine as chromogenic agent. The research about content of amylose and amylopectin in the sample with the standard curve had been worked out.According to the experiment,the RSD were 0.27% and 0.63% respectively,recovery data were 96.18% and 97.89%,while detection limit were 0.09 mg / L and 1.58 mg / L based on the amylose and amylopectin test. Appending accuracy analysis,allconfirmed that the dual- wavelength determining the content of amylose and amylopectin had more accurate effect.