Bench-scale test was employed to study the biogas yields of anaerobic fermentation on cyanobacteria. The results indicated that, after 7 days’ decomposition at 30~35°C, fresh cyanobacteria achieved the highest biogas generation efficiency. 246mL/gCOD of biogas was produced at 35°C of fermentation temperature, with a biogas yield potential of 354mL/g(VS). After 15-day anaerobic reaction, the cumulative biogas, COD and VFA concentration tended to be stable. The activities of amylase and dehydrogenase were inhibited at the early stage of anaerobic reaction, while the activity of protease and the concentration of coenzyme F₄₂₀ increased gradually, reaching to 27.66µmol/(gVS·min) on the 6^th day and 0.62µmol/g(VS) on the 15^th day, respectively. The period of 15 to 18 days was favorable for the anaerobic fermentation of decomposed cyanobacteria, which was less than that of anaerobic digestion with fresh cyanobacteria as stroma. The process of cyanobacteria decomposition promoted the anaerobic reaction, and 7-day decomposition of cyanobacteria promoted microbial activity and methane generation potential.