In the research， a mixed bacterial biofilm formed by foodborne pathogens （Staphylococcus aureus， Escherichia coli and Salmonella enterica） was used as a research object. After qualitative and quantitative detection， Real Time PCR method was used to detect single and mixed bacterial biofilms. Changes in the transcriptional levels of 28 toxin genes of Staphylococcus aureus was studied by Real Time PCR method. The results showed that the crystal violet staining method， silver staining method and scanning electron microscopy method all proved that the mixed bacteria reached the maximum adhesion when cultured for 24 h；the number of viable bacteria of the three bacteria in the mixed biofilm was lower than that of the single bacteria. The number of the toxins， 28 toxin genes were detected in Staphylococcus aureus；mixed bacteria compared to single bacterial biofilm， the up-regulation of the enterotoxin gene sep， ser， significantly decreased hemolysin hla and ecdysone etd The enterotoxin seb is expressed in equal amounts.