Abstract: A ultra high performance liquid chromatography tandem mass spectrometry(UPLC-MS/MS) method was developed for determining diafenthiuron residues in orange and soil.The dissipation curve and final residues of diafenthiuron at PHIs were studied.The samples were extracted with acetonitrile,cleaned with N-propylethylenediamine(PSA) and detected with UPLC-MS/MS.The fortified recoveries ranged from 84% to 89% with relative standard deviations of 2.6% to 7.2% in whole fruit,flesh and peel,from 83% to 86% with relative standard deviations of 2.2% to 5.6% in soil when diafenthiuron was spiked at 0.01,0.1 and 1 mg/kg levels.The results of residue dynamics indicated that the half-lives of diafenthiuron in orange and soil were 3.7-4.4 d and 4.1-5.4 d,respectively.The orange was sprayed with 500 g/L SC at dosage 500-750 mg/L(2-3 times) at young fruit period,the interval period was 10-14 days,the final residues of diafenthiuron were all below the 0.01 mg/kg in flesh at the 21st day after last application.The residue of whole fruit was below the maximum residue limit(MRL) set by China(0.2 mg/kg).