The difference of allelpphthic effect for 120 accessions of different rice germplasm on barnyardgrass were evaluated by using field test and treatment of leaf extracts.The result showed that there were significantly difference of allelopathic effect potential among rice germplasm groups,especially under the field conditions.The order of control effect on barnyardgrass growth was traditional variety>improved variety>introduced foreign variety>hybrid rice,and the value of relative factors of allelpphthic effect on seedling fresh weight and seedling dry weight of barnyardgrass was larger than that of relative factors of seedling height.According to the result of leaves water extract experiment in lab,the control effect of traditional variety on barnyardgrass growth was stronger,although the difference of allelpphthic effect were smaller among rice germplasm groups,and control effect on root length of barnyardgrass was bigger than that on seedling height.The frequency of higher allelopathic varieties in traditional variety was higher than that of other germplasm groups.Therefor it is very important to evaluate the allelpphthic effect of traditional variety in the future.