Abstract: UHPLC was applied to the determination of metolcarb, isoprocarb, baycarb and diethofencarb in water with solid phase extraction. The water sample (preadjusted to pH 4-5) was purified by passing through Oasis HLB-solid phase extraction column and eluted with methanol. Eclipse XDB C18 chromatographic column was used as stationary phase at column temperature of 30 ℃, and a mixture of methanol and water (70+30) was used as mobile phase. UV-detection at 284 nm was adopted in the determination. Linear relationships between values of peak area and mass concentration of the 4 pesticides were kept in definite ranges, with detection limits(3S/N )in the range of 0.049-1.6 μg·L-1.Tests for recovery were made at 3 concentration levels, giving values of recovery in the range of 92.0%-106 %with RSD′s (n=7)in the range of 1.2%-4.9%.