Abstract:The method of the root length or shoot length of maize root length of the activity of acetochlor was employed in studying the effects of fulvic acid (FA) on acetochlor bioactivity and persistence. The results indicated that the dosage of acetochlor had significant negative linear correlation with the root length and shoot length of maize, the regression equation of root length was y1=0.098x</em>1+9.449, R1= -0.9916, the regression equation of shoot length was y2=0.079x2+22.255, R2=-0.9809. The bioactivity of acetochlor on the root length and shoot length of maize was respectively improved 7.12%-14.27% and 6.32%-11.65%, the persistence of acetochlor was prolonged 0.46-12.17 days by dosages 0.25%-4.00% of FA. 28 days after application, the fresh weight inhibition rate of acetochlor on barnyardgrass was improved 11.93%-16.88% by dosages 0.5%-2.0% of FA.