Objective To analyze an outbreak of foodborne disease caused by Salmonella typhimurium, and to study the molecular characteristics of the pathogen through laboratory detection and similarity analysis, so as to provide scientific basis for clinical diagnosis and treatment, incident traceability, prevention and control. Methods The collected samples were screened and detected by the FilmArray multiplex PCR system, and the pathogens were identified by mass spectrometry and serotyping. Antibiotic susceptibility tests, pulsed field gel electrophoresis (PFGE), and whole genome sequencing were performed on the isolated strains. Sequence type (ST), cgMLST, and rMLST were obtained by comparing the MLST of Salmonella and performing cluster analysis. The isolates were studied for genes that are related to drug resistance and virulence. Results A total of 15 Salmonella strains were isolated, including 3 from suspected food sources and 12 from the patient's feces, and all of them were Salmonella typhimurium. The PFGE pattern showed two patterns, 12 strains from stool and 2 strains from suspected food had the same pattern, the similarity was 100%, and the similarity of the other one strain from suspected food was 88.89%. The 15 isolates were categorized into either ST19 or rST-138396 (new) type. The cgMLST and wgMLST core genome loci varied from 1 to 15 and 1 to 395, respectively. The drug resistance spectrum of 15 isolates was as follows: Ampicillin-Ampicillin/Sulbactam-Cefazolin-Cefotetan-Amikacin-Gentamicin-Tobramycin-Levofloxacin-Furatoin-Streptomycin-Nalidixic Acid-Tetracycline-Chloramphenicol; The genome of the strains contained 13 related drug resistance genes and 271 known virulence genes. Conclusion This foodborne disease outbreak was caused by Salmonella typhimurium from the same source and with the same molecular typing characteristics. The isolated Salmonella typhimurium was capable of producing extended-spectrum β-lactamases and was resistant to 13 antimicrobials, indicating that it was a severe multi-drug resistant strain.