[Background] Pig digestive tract disease is one of the most important diseases in the pig industry and brings certain economic losses to the swine industry. Escherichia coli is a common pathogen causing diarrhea of pigs at different ages, but mainly in young pigs. [Objective] The purpose of this study was to isolate and identify pathogens causing large-scale diarrhea in pigs on a large-scale pig farm in Meishan City, Sichuan Province. [Methods] Bacteria were isolated and identified from the infected pig liver, stomach and contaminated feed using conventional bacterial isolation methods combined with 16S rRNA gene sequence analysis. The isolates were tested for pathogenicity in mice, 16S rRNA gene phylogenetic analysis, virulence genes, and drug sensitivity testing. [Results] One pathogenic Escherichia coli was isolated from the liver of diarrhea pigs, one strain of Bacillus cereus was isolated from the stomach, and the source of infection was traced back to the feed on the farm. By detecting the corresponding virulence genes of these two strains, it was found that Escherichia coli is not extra-intestinal pathogenic type. Bacillus cereus was detected to have five virulence genes: nheA, nheB, nheC, bceT, entFM; Aminoglycosides and cephalosporins have good antibacterial effects on Escherichia coli. Erythromycin, florfenicol, cephalexin, cefoperazone have good antibacterial effect on Bacillus cereus, but the bacteria were not sensitive to conventional antibiotics such as penicillin and amoxicillin. [Conclusion] Feed is contaminated by Escherichia coli and Bacillus cereus.