Abstract: OBJECTIVE To investigate the correlation between the formation of tongue coating and the tongue coating flora. METHODS A hospital-based case-control study was developed with 47 new patients with gastric cancer (GC) as cases and 42 healthy people as controls. The tongue coating flora was measured by 454 high-throughput pyrosequencing based on 16S rRNA gene. Multi-factor correlated analysis was conducted between the tongue coating and the tongue coating flora. RESULTS The richness and diversity of the tongue coating flora showed no correlation with the coating color or the coating nature in both the cases and controls. 31 taxa (1 classes， 6 orders， 9 families and 14 genera) and 10 taxa (1 orders， 3 families and 6 genera) showed significantly different between the white coating and yellow coating in the cases and controls， respectively (P<0.05). However， only 5 taxa (1 order， 1 family and 3 genera) and 2 taxa (1 family and 1 genus) were observed significantly different between thin coating and thick coating in the cases and controls， respectively (P<0.05). The relative abundances of Bradyrhizobiaceae and Delftia in the yellow coating were distinctly higher than that in the white coating (P<0.05). The ratio of significantly negative correlations of the bacterial genera between the white coating and yellow coating was obviously higher than that in the white coating or that in the yellow coating， and similar phenomenon was observed in the tongue nature. Based on the bacterial function prediction of the tongue coating， the function purine metabolism was significantly higher in GC patients with yellow coating than that with white coating (P<0.05)， which was confirmed by the serum uric acid level. Meanwhile， the function lipid metabolism was stronger in the controls with thick coating than that in the controls with thin coating (P<0.05)， which was confirmed by the serum total cholesterol level. CONCLUSION The structure of tongue coating flora shows stronger impact on the coating color than the coating nature， and the symbiotic correlation in the tongue coating flora may reflect the scientific connotation of TCM syndrome differentiation of tongue coating.