A method for the simultaneous screening and determination of 248 pesticide residues in apples and lettuces was developed by liquid chromatography coupled with high resolution quadrupole time-of-flight mass spectrometry(LC-Q TOF/MS).The samples were extracted with 10 mL acetonitrile and 5 mL 0.1%(by volume) acetic acid,cleaned up by a modified QuEChERS method.Confirmation was achieved by electro-spray ionization(ESI) in positive mode using SWATH MS acquisition,and quantification was carried out by external standard method.Two databases of accurate mass and fragment ions were created.The standard matrix-matched calibration curves of 248 target compounds were linear in the range of 0.010-0.200 mg/L,with the correlation coefficients(r) larger than 0.99.The limits of quantification for 248 target compounds all were 0.010 mg/kg.The mean recoveries for the target compounds at three spiked levels of 0.010,0.050，0.100 mg/kg ranged from 25.2% to 128%,32.4% to 132%and 28.9% to 133%,respectively with relative standard deviations of 0.98%-21.2%(n=6).With the advantages of simplicity,timesaving,high sensitivity and good stability,the method was applicable for the simultaneous screening and determination of 248 pesticide residues in apples and lettuces,and could significantly reduce the test cost.