At the end of August 2020，a large number of bobbed and castrated piglets acutely died in a farm in Jiangsu Province，lasting for about 2 months. In order to confirm the causes leading to such death，4 infected piglets sent for inspection were autopsied for laboratory diagnosis in mid-November. Initial diagnosis was made according to epidemiological history，clinical symptoms，necropsy lesions，and the results of blood smear and visceral contact plate，followed by confirmation through bacterial and molecular biological detection. The results showed that yellow and septic changes were observed in most lesions，and a large number of spherical and round blue-purple bacteria were observed through visceral contact plate examination；the bacteria isolated and purified from the lesion tissues were identified as Staphylococcus haemolyticus through 16S rRNA sequence alignment；it was found that，through blood smear examination，a large number of red blood cells were deformed with star-shaped，serrated，half-moon and other irregular shapes，which were consistent with the characteristics of Eperythrozoon，and specific bands were amplified by PCR. It was finally confirmed that the death of piglets in the large-sacle farm was caused by co-infection with Eperythrozoon and Staphylococcus hemolyticus. The outbreak was effectively controlled after 5 days since target administration was conducted according to diagnosis results. Modern molecular biology methods and classical detection methods were used to diagnose the case，which played an important role in the diagnosis of co-infection.