To investigate the generation and occurrence mechanism of viable but non-culturable（VBNC） in Salmonella enterica serovar Typhimurium artificially inoculated in BPY broth during thermosonication （TS）， RT-qPCR and plate counting methods were used to detect the viable and VBNC state S. Typhimurium， ESR was used to detect free radicals generation. The relationship between free radicals generation and VBNC state incidence index was analyzed. Generally， higher intensity of TS treatment promoted S. Typhimurium into VBNC state and produced more free radicals. Three kinds of free radicals were detected， including C-centered radicals， hydroxyl radicals and hydrogen radicals. There was a correlation between the intensity of free radicals and the VBNC state incidence index during TS treatment， which can be fitted and validated using the Boltzmann model. Sodium pyruvate， as a free radical scavenger， was used to confirm that free radicals play an key role in inducting VBNC state microbial cells. These obtained results may help to facilitate application of TS processing.