[Background] Tarcoidosis in Trionyx sinensis occurred in a Trionyx sinensis farm in Liaocheng, Shandong, causing nodules in the viscera organs and limb muscles. Multiple infections occurred at the late stage of sarcoidosis and all viscera were stinky and rotten. According the survey, the infectious rate and mortality increased in 2017 compared with 2016. However, until now, no any report can be found on sarcoidosis in Trionyx sinensis in China. The route of infection, the pathogen, the method of prevention and control of sarcoidosis in Trionyx sinensis are unknown. [Objective] Our study aims to prevent sarcoidosis through analyzing the pathogeny of sarcoidosis in Trionyx sinensis and studying the pathematology. [Methods] According to disease diagnosis methods, separation and identification of pathogen were done after excluding parasites and virus infection. Meanwhile, in vitro sensitivity tests for pathogenic bacteria were used to screen sensitive drugs and to study the histopathology of the disease. [Results] Two dominant strains, DM1 and DM2, were isolated from the lesion and DM1 was the pathogenic bacterium of sarcoidosis in Trionyx sinensis according to regression infection tests. DM1 was Salmonella typhimurium through 16S rRNA gene sequencing and physiological-biochemical identification. The drug susceptibility analysis showed that pathogenic bacterium was sensitive to 14 antibiotics such as amikacin, gentamicin, cefoperazone, ciprofloxacin, and moderately sensitive to furazolidone and cephaloprim, but resistant to 18 antibiotics such as norfloxacin, rifampicin, ampicillin. Pathological section showed that the outer layer of the nodule was the capsule formed by fibrous connective tissues and the internal bean dregs like substance was eosinophilic coagulating necrosis. [Conclusion] Salmonella typhimurium was the pathogen of sarcoidosis in Trionyx sinensis and it can be prevented during the breeding process by feeding amikacin, gentamicin and similar antibiotics.