Abstract: In order to determinate microcystins fast and sensitively,an electrochemistry determination method of differential pulse voltammetry was established with bi- modified gold nanoparticles. The bi- modified gold nanoparticles were prepared by modifying gold nanoparticles with mono- 6- thio- β- cyclodextrin and thiol phosphate based on the structural characteristics of microcystins. The bi-modified gold nanoparticles had an absorbance capability of 2.125 μg/m L and a static allocation coefficient of 5.67,respectively. Then microcystin was determined with the electrochemical sensor prepared with a glassy carbon electrode which modified with toluylene red polymer to get a positive charged surface for absorbing the bi-modified gold nanoparticles. The result showed that this method had a strong resisting interference ability with a linear range of determination from 26 nmol/L to 213 μmol/L and a detection limit of 19 nmol/L,respectively.