Pot culture experiments were conducted to examine the effects of water irrigation and rice plant density on the interference of allelopathic rice on barnyardgrass (Echinochloa crus-galli). The results showed that under water irrigations, allelopathic rice cultivars Xiayitiao, Gumei 2 and Zhong 156 significantly reduced the plant height of barnyardgrass than non-allelopathic rice cultivars Xiushui 63 and Chunjiang 11. Barnyardgrass plants grew shorter as rice plant density increased. Allelopathic rice cultivars Jizaoxian and Gumei 2 interfered with barnyardgrass, even at their densities as low as 4 plants per pot, and the interference reduced plant height of barnyardgrass significantly compared with the non-rice control. Allelopathic rice cultivars Xiayitiao, Jizaoxian, PI312777, TN1, Gumei 2 and Zhong 156 at 32 rice plants per pot inhibited the growth of barnyardgrass significantly than Chunjiang 11.