Abstract: To evaluate the residue risk and safety of pydiflumetofen in tomato, an analytical method based on ultra-high performance liquid chromatography with tandem mass spectrometry (UPLC-MS/MS) was developed, and the dissipation and residues of pydiflumetofen under different planting modes were investigated. Moreover, the dietary risk assessment was conducted based on the dietary consumption and residue datas. The results showed that the linearity was acceptable in the range of 0.010-2.0 mg/L with r > 0.99. At the spiking levels of 0.010, 0.10, 0.50 and 1.0 mg/kg, the average recoveries ranged from 92% to 108% with the relative standard deviations (RSDs) of 2.9%-8.1%, and the limit of quantification was 0.010 mg/kg. The residue dissipation of pydiflumetofen in tomato in Beijing, Hainan and Shandong were in accordance with the first-order kinetic equation, and the half-lives were 11.4, 11.4 and 7.1 d, respectively. The final residues at the pre-harvest interval of 5 days were lower than the maximum residue limits (MRL) in the United States, Japan and Codex Alimentarius Commission (CAC). The short-term dietary exposure risks to children aged 1-6 and to the general population in China were 1.8%-2.8% and 0.6%-1.0%, respectively, which were all lower than 100% and indicated that there were no un-acceptable dietary exposure risk to different populations. The results provide scientific suggestions for the rational use and establishment of the MRL of pydiflumetofen on tomato in China.