Objective Research the relationship between the oral Thrichomonas and the periodontal disease. Methods We should divide the choosen objects into the non-periodontal disease, gingivitis, periodontal disease andnecrotic gingivitis. Take the serumal tartar from the inflammation gingivas to make the fresh smear.Compare the results the check with the x2 test. Results In the non-periodontal disease, gingivitis, periodontal disease and necrotic gingivitis,the rate which were infected with oral Thrichomonas each is 0.00%(0/126),49.15% (58/118),42.55%(80/118),85.65%(94/110).The rate of the necrotic gingivitis is higher than the non-periodontal disease, gingivitis and periodontal disease (P<0.005 ). The rate of the gingivitis and periodontal disease are higher than the national parasites(P<0.005). There are no differences between the gingivitis and the periodontal disease (P>0.05). The reat of the gingivitis and periodontal disease are higher than the national parasites(17.4%)(P<0.005). The rate of the national parasites is higher than non-periodontal disease (P<0. 005). Conclusion The relationship is closed between the infection of the subgingival oral Thrichomonas and the periodontal disease. Key words: Oral thrichomonas; Infection; Periodontal disease