Abstract: Objective To investigate the distribution of 3 bacteria（P. subgingivals,T.forsythia and T.denticola） in subgingival plaques of naval officers and soldiers on warships after a long voyage and their pathogenesis. Methods Subgingival plaque samples were collected from 80 naval officers and soldiers on warships. The subjects were divided into 3 groups according to their gingival index（GI）. The GI of the 3 groups was 0, 1, and 2 or 3, respectively. Distribution of the 3 bacteria in subgingival plaque samples were detected by polymerase chain reaction（PCR）. Results The prevalence of the 3 bacteria was 19.05%, 52.38% and 19.50%, 18.75%, 65.63% and 40.63%, and 18.52%, 81.48% and 44.44%, respectively, in groups 1, 2 and 3. No difference was found in the prevalence of P. subgingivals among the 3 groups（P＞0.05）. The prevalence of T.forsythia and T.denticola was significantly higher in groups 2 and 3 than in group 1（P＜0.05）. Conclusion Infection with P. subgingivals or T.forsythia alone or both is related with gingivitis in naval officers and soldiers after a long voyage