Abstract: The pot experiment was used to study the effect of mutual competition on the morphology characteristics of cultivated rice and weedy rice. Weedy rice and cultivated rice were planted in the same basin, in accordance with the ratio of 2:1 and 1:2, respectively, and treatments in which weedy rice or cultivated rice was planted alone in one basin were used as control. Tiller numbers, plant height, leaf length and width, dry matter accumulation and root traits of weedy rice and cultivated rice were measured. The results showed that the plant height and leaf morphological characteristics were less affected, but the tiller numbers, dry matter accumulation and root traits of the cultivated rice ‘Shennong 265’ were negatively and significantly affected because of the competition of weedy rice and cultivated rice. The tiller numbers, plant height, leaf morphological characteristics, dry matter accumulation and root traits of the weedy rice ‘WR04-12’ were increased or improved under the competition, but did not reach the significant level. In addition, the tiller numbers, plant height and root traits of weedy rice ‘WR04-12’ were higher or better than those of the cultivated rice ‘Shennong 265’ in the same growth period, so the weedy rice ‘WR04-12’ occupied the advantageous position in the competition, while the cultivated rice was in disadvantageous position shaded by weedy rice. Therefore, the competition of weedy rice and cultivated rice limited the growth and dry matter accumulation of the cultivated rice ‘Shennong 265’, and led to yield reduction.