Abstract: The result of the test in laboratory showed that the toxicity of abamectin against Pieris rapae (L.) was very high (the LC50 was 0.022 mg/L), the toxicity against Plutella xylostella (L.) (the LC50 was 0.12 mg/L) and Lipaphis erysimi (Kaltenbach) (the LC50 was 0.28 mg/L) was less. That the toxicity of the pesticide was quite bad against Spodoptera exigua (Hübner) and Prodenia litura Fabricius, the LC50 was 67.56 mg/L and 165.73 mg/L, and that the pesticide could not kill the eggs of Plutella xylostella (L.) and the activity to young larvae reduced with increase of larvae age. The result of trial in field stated that control effects of abamectin to Pieris rapae (L.) and Plutella xylostella (L.) at 4 mg/L and 8 mg/L was over 95% and the high effectiveness was maintained for 10~15 days. The binary mixtures of abamectin+beta-cypermethrin(1∶6) and abamectin+monosultap(1∶299) showed synergic activity to Plutella xylostella (L.) and good effect against Pieris rapae (L.) and Plutella xylostella (L.) in field.