Methylene blue, as a dye, has been widely used in industry, medicine, aquaculture, skin care, and et al. But excessive use of methylene blue, not only pollutes the environment, but also endangers the health of human beings and animals. In this paper, ratio-fluorescence detection system has been founded through mixing of graphene and CdTe quantum dots, and a method for quantitative analysis of MB is founded based on linear relationship between variety of fluorescence intensity and concentrations of methylene blue, of which linear range is 3.13 - 9.38 nmol/L and the lowest detection limit is 0.5589 nmol/L. This method have good sensitivity, selectivity and stability, could be used for more accurate detection of methylene blue.