Using the selective medium with carboxymethyl cellulose (CMC) as the sole carbon source, through direct screening and screening after enrichment, separation, purification as the preliminary screening methods, and the transparent circle method and shake flask fermentation as the second screening methods, two strains of cellulase-producing microorganisms with higher cellulase activity, MA35 and MC, were screened out from intestines of Megalobrama amblycephala and Ctenopharyngodon idellus. 16S rDNA/ITS molecular identification and morphological observation showed that:MA35 from Megalobrama amblycephala belonged to Aspergillus niveus, MA1 from Megalobrama amblycephala and CI10 from Ctenopharyngodon idellus were actually identical bacteria, MC, belonged to Aeromonas veronii. Fermentation trend studies indicated that MA35 had a higher extracellular and intracellular cellulase activity compared to MC. This study not only screened out cellulase-producing strains from the intestines of Ctenopharyngodon idellus, but also isolated a new cellulase-producing strain from Chinese unique aquatic organism Megalobrama amblycephala, providing a scientific research basis for the rational aquaculture of herbivorous fish and the dietary ratio of fish feed.