Fluroxypyr-mepthyl,as an efficient herbicide,is widely used to control broad-leaf weeds in wheatland.For the safe and rational use of this herbicide on wheat,the dissipation trend,terminal residue levels,and risk assessment of both fluroxypyr-mepthyl and fluroxypyr were investigated under field conditions.This study developed and validated a modified quick,easy,cheap,effective,rugged,and safe(QuEChERS)method for simultaneous determination and quantitative analysis of fluroxypyr-mepthyl and fluroxypyr residues in wheat grain,straw and soil samples using liquid chromatography-tandem mass spectrometry(LC-MS/MS).The mean recoveries ranged 77~110%at the level of 0.05~0.5 mg kg-1 with the RSD < 6%in all wheat samples,and the limit of qualification(LOQ)for fluroxypyr-mepthyl and fluroxypyr was both established as 0.05,0.05,0.1,0.1 mg kg-1,respectively for wheat grain,seedling,straw and soil matrices.From residue trials at three geographical experimental plots in China,the results demonstrated that fluroxypyr-mepthyl and fluroxypyr dissipated with half-lives of 5.1~8.6 days in wheat seedling and 2.0~4.6 days rapidly in soil,respectively.At harvest time,the terminal residues in wheat grain samples were found to be all below 0.05 mg kg-1,based on the application rate(150 g a.i./ha)and the pre-harvest interval(PHI,2 days)recommended by the manufacturer,which were far lower than the maximum residue limit established in China(MRL,both 0.2 mg kg-1 for fluroxypyr-mepthyl and fluroxypyr).The results suggest that the use of fluroxypyr-mepthyl and fluroxypyr on wheat is considered to be safe under the Good Agricultural Practices(GAP)in the Chinese fields.Risk assessment for different groups of people in China was evaluated with result showing that there was no significant health risk for consumers via grain consumption.