Gut microbiota has been implicated as a critical role in the development of colorectal cancer (CRC) and colorectal adenoma (CRA). However, few basic research has revealed the association between gut microbiota and the development of CRA and CRC. We aim to compare the diversity and composition of intestinal flora in CRA and CRC patients, to reveal the changes of intestinal microorganism in the evolution of normal intestinal mucosa-CRA-CRC axis, and to explore potential biomarkers. We analysed colorectal tissues (11 CRC, 11 CRA and 11 healthy volunteers (HC). Using 16S rRNA sequencing analysis to compare the gut microbiome of patients with CRC, CRA and HC. The microbial diversity including alpha diversity, beta diversity and identified the microbial compositions among the three groups were characterized. Intestinal microbial composition and diversity were significantly decreased in the CRA group, whereas those were obviously increased in the CRC group. The fourth most predominant microbial compositions in the three groups were Proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes at the phylum level. Moreover, the relative abundance of Fusobacteria at the phylum level behaved a general trend of decreasing in CRA group first and then increasing in CRC group. When exploring the Fusobacteria abundance in MetaCyc database signaling in different groups, it was indicated that Fusobacteria was also higher in CRC than CRA especially in the ICME2-PWY, Cobalsyn-PWY and Anaglycolysi signal pathways. Taken together, the observed intestinal microbial difference among the three groups provides a basis for understanding the potential role of intestinal microorganism in the evolution of normal intestinal mucosa-CRA-CRC axis.