Abstract: In order to explore the main reason of quickly degradation for pesticides in field vegetables,the study of imidacloprid was carried out to research the differences of the residue in Brassica rapa L.Chinensis Group.under different simulated rainfall intensity,rainfall interval and different pesticide formulations of several conditions.The results showed that the residues of imidacloprid in B.rapa reduced gradually along with the increase of rainfall intensity,increased accordance with the rainfall interval,reduced with the increasing of rainfall frequency,and the effect of continuous rainfall on leaching of imidacloprid was larger than intermittent rainfall.Meanwhile,the residuesof imidacloprid were different in two different pesticide formulations,the leaching rate of rainfall for WP was higher than EC.