Abstract: Field experiments were conducted to study decline and final residue of bensulfuron methyl·pretilachlor 2 g/kg granule in paddy field.Paddy water,chaff,rice straw and rice plant sample were directly extracted with dichloromethane,paddy soil were directly extracted with V(dichloromethane):V(methanol)=9:1 mixture,brown rice were extracted with V(dichloromethane):V(methanol)=7:3 mixture and dichloromethane.The residue of pesticides was detected by HPLC.The results showed that when the spiked levels were 0.05 to 1 mg/kg(mg/L),the average recovery of bensulfuron methyl and pretilachlor ranged from 75% to 103% with relative standard deviation of 1.6%-13%;the limit of detection(LOD) of bensulfuron methyl and pretilachlor were 0.02 mg/L,the minimum detectable amount were 4.0×10-10 g,and the limit of quantification(LOQ) were 0.001 mg/L in paddy water,0.005 mg/kg in paddy soil,0.01 mg/kg in rice plant,chaff and brown rice.Decline study was done by spraying with a high dose(270 kg/hm2,bensulfuron methyl active ingredient was 67.5 g/hm2,pretilachlor methyl active ingredient was 472.5 g/hm2) by direct scatter method after rice was transplanted in 5-7 days,and the final residual test carried out with a low dose (180 kg/hm2, bensulfuron methyl active ingredient was 45 g/hm2,pretilachlor methyl active ingredient was 315 g/hm2) and high dose(270 kg/hm2). The results showed that the half-lives of bensulfuron methyl were 5.06 to 5.83 days in water,9.76 to 11.55 days in soil and 4.52 to 4.82 days in plant,and the half-lives of pretilachlor were 5.94 to 6.45 days in water,7.70 to 9.90 days in soil and 4.11 to 4.89 days in plant.The final residues of bensulfuron methyl and pretilachlor were not detected in normal harvest brown rice.