In order to solve the problems including unideal biomass of algae in the algal biofilm and constrain of strong light,the biofilm matrix of attached diatom(Cocconei sp.)was screened,and the constructed Cocconei can-vas mesh biofilm with the attached diatom at density of 1 ×105 ind/mL was cultured in F/2 medium at light intensity of 0,1,8,18,54,90 and 126 pmol/(m2·s)at temperature of(20±2)℃ and the light period of 12 L:12 D for 9 days,and then,the effect of illumination intensity on the absorption of ammonium nitrogen at concentration of 0,20,60 and 100 mmol·L-1 and the growth of the algae subsequently in this biofilm.The results showed that coarse linen and canvas mesh were more conducive to the apposition growth of Cocconei sp.(P<0.05),with the maximal biomass of(1.80±0.52)× 106 ind./mL in canvas mesh.The significant variation in absorption effect of Cocconei sp.on ammonium nitrogen was found under different illumination conditions(P<0.05),with absorption rate of 98.5%by Cocconei sp.at ammonium nitrogen concentration of 20 mmol/L,at illumination intensity 54μmol/(m2·s)in 96 h.Meanwhile,the absorption rate of 86.7%was observed at ammonium nitrogen concentra-tion of 60 mmol/L,with the Cocconei sp.harvested biomass of(2.90±0.12)×106 ind./mL,and the carotenoid con-tent of(0.520±0.013)mg/mL,which could be used as high quality forage for aquatic animals.The results showed that the substrate was more conducive to the adhesion of Cocconei sp.,and the alga biofilm grew in a wide range of light,and had a good ammonia nitrogen absorption capacity of up to 98.3%at light intensity of 18-54 μmol/(m2·s).Therefore,the alga biofilm obtained in the present experiment has good application value.