The N-doped active carbon prepared by high-temperature carbonization of Cyanobacterial blooms (CBB) is used to aerobic oxidation of 5-hydroxymethylfurfural (HMF), thus developing a green catalytic technology for 2,5-diformylfuran (DFF) synthesis, while disposing cyanobacterial blooms as a resource. The prepared N-doped active carbon（N-AC-CB）was characterized by XRD、Raman、BET、XPS and FT-IR methods, and used as a catalyst for aerobic oxidation of HMF to DFF. The effects of carbonization temperature of CBB and reaction conditions on the reaction were investigated. The results show that: the N-AC-CB-700 obtained by carbonization of CBB at 700℃has good catalytic performance, and the graphite- type nitrogen hybrid structure contained in it plays an important role in the formation of catalytic active centers; Under the catalytic action of N-AC-CB-700, 92.8% yield of DFF was achieved with HMF complete conversion. After the catalyst reused 7 times, the activity only decreased by 5.4%, and after reused 9 times, the activity decreased by 13.3%.