Abstract: To study the response of different oat varieties to pendimethalin of different concentrations, the root tip was treated by different concentrations of pendimethalin, then the condition of mitosis was observed; 6 oat varieties were planted in field to study the effect of pendimethalin on oat growth; at last, the antioxidase activity was detected. The results showed that chromosome would agglutinate, move slowly, reduplicate or have binucleated cell. When the concentration of pendimethalin was higher than 0.01 μg/mL, the percentage of abnormal cells increased rapidly. The pendimethalin of 2250 mL/hm2 had no influence on the plant height of ‘Bayou 6’and‘Bayou 9’, while had negative effect on the plant height of‘Bayou 1’,‘Bayou 3’,‘Baiyan 2’ and‘Bayan 4’, and the yield change among the varieties was different. The activity of four antioxidant enzymes under 1650 and 3000 mL/hm2 pendimethalin treatment was little higher than that of CK. Oat root tip cell fission would be abnormal under pendimethalin treatment, different oat varieties had different sensibilities to pendimethalin. The change of antioxidant enzyme activity in oat plant was of different degrees, and through those changes, oat could reduce the damage of pendimethalin to plant.