Abstract: The field residue decline study and final residue trials of pyrimethanil and diethofencarb in spring welsh onion in Shandong Province,China,were designed.Welsh onion samples were extracted with acetonitrile and the extracts were cleaned up by SPE column filled with mixed type SAX-PSA,followed by determination with GC-MS at selected ion monitor mode(SIM).The fortified recovery at level of 0.001 to 0.1 mg/kg and 0.01 to 0.1 mg/kg ranged from 97.8% to 107.2%,with relative standard deviation of 2.7% to 7.4%.The limit of detection for pyrimethanil and diethofencarb in Welsh onion were 0.000 3 and 0.003 mg/kg,and the limit of quantification Welsh onion was 0.001 and 0.01 mg/kg,respectively.The field residue dynamics study showed that the half-lives of pyrimethanil and diethofencarb in Welsh onion was 4.1 d and 3.1 d,respectively.When it was sprayed for 2 to 3 successive times at application dose and at double dose ,at 7 th,14 th and 21 th day after the last application,the final residues of pyrimethanil and diethofencarb in Welsh onion were between 0.007 to 0.560 mg/kg and ND to 0.394 mg/kg,respectively,which were below the MRLs of Japan.