Direct discharge of waste liquid containing methylene blue（MB） will cause serious water pollution.In order to study the adsorption performance of activated carbon for methylene blue,agricultural waste sunflower was used as raw material and H₃PO₄ as activator to prepare powdered activated carbon（PAC） and block activated carbon（BAC）,and the adsorption per-formance of PAC to MB was studied.The hole structure and surface properties of activated carbon were analyzed by means of surface area test（BET）,X-ray photoelectron spectrum（XPS）,X-ray diffraction（XRD）,infrared spectroscopy（FT-IR） and scanning electron microscopy（SEM）.The research results showed that the shape of activated carbon precursor had great in-fluence on the microstructure of activated carbon.PAC had larger specific surface area and total pore volume than BAC （701.95,566.49 m²/g and 2.23,1.04 cm³/g,respectively）.The average pore size of PAC and BAC was 7.31 nm and 12.66 nm,respectively.Both PAC and BAC had the structural characteristics of mesoporous materials.There were abundant oxygen-co-ntaining functional groups and a large number of loose amorphous carbon on the surface of both activated carbons,and the existing metaphosphate played a supporting role on the pores,which provided more active sites and adsorption channels for the adsorption of MB.The results of the adsorption experiment showed that the maximum adsorption rate was 72.2% under the conditions of 100 mL MB solution with a concentration of 200 mg/L,pH of 8 and PAC dosage of 50 mg at 25 ℃.The adsorp-tion process was conformed to the pseudo-second-order kinetic model,the intra-particle diffusion model and the Langmuir isotherm adsorption model.