A 69-year-old male patient with pleural effusion and pulmonary infection was treated in Jiangxi Provincial people’s Hospital on October 17th, 2021. The patient complained of pain in the right costal arch for 7 days, with a history of periodontal disease and a personal history of cerebral infarction. Physical examination upon admission showed dullness on percussion at the right chest, the right lung breath sound was not heard, and dry rales could be heard in the left lung. Chest Color Doppler Ultrasound revealed bilateral pleural effusion; chest X-ray and CT showed right pleural effusion and right lung infection. Trichomonas could be seen in hydrothorax smear and Wright-Gibbs smear. High-throughput sequencing of pleural effusion showed Trichomonas oralis. Combined with the patient’s history and auxiliary examination results, the diagnosis was oral Trichomonas infection and pulmonary infection. During hospitalization, patients were given closed thoracic drainage, intravenous infusion of metronidazole and ornidazole (0.5 g/once, twice a day) and intrapleural injection of metronidazole and ornidazole (0.5 g/once, once a day) for 14 days combined with piperacillin tazobactam (4.5 g/once, 3 times a day) for 23 days, and urokinase (200 000 units/time) on October 30th and October 31st, respectively. After three times of intrapleural injections to eliminate pleural separation on November 2nd, the patient’s symptoms improved and no trichomonas was found in pleural effusion. Chest CT indicated that the pleural effusion was significantly improved, and the patient was discharged without additional abnormality. One month after discharge, the patient had no discomfort, no pleural effusion and no obvious abnormality were found by chest CT examination.