Abstract: In this paper, five oxygenic terpenoids — (-)Carveol (C₁₀H₁₆₀), (+)Carvone (C₁₀H₁₄₀), (-)Menthone (C₁₀H₁₈₀), (-)Carvyl acetate (C₁₂H₁₈₀₂) and (+)Cedrol (C₁₅H₂₆₀) were used as test compounds and barnyardgrass(Enchinochloa crusgalli L.) receptor in rotational regression design experiment. The objective was to analyze allelopathic effect of oxygenic terpenoid on barnyardgrass. The results show that the main effects of (-)Carveol, (+)Carvone, (-)Menthone and (-)Carvyl acetate have an downward parabolic curve, while (+)Cedrol shows the opposite. Boundary effect of single factor indicates that, when single factor concentration falls below -2, the inhibition trend of the oxygenic terpenoids on barnyardgrass root length follows the order of: (-)Menthone >(-)Carveol>(+)Carvone>(-)Carvyl acetate>(+)Cedrol. When the single factor concentration is above +2, the order of inhibition trend of the oxygenic terpenoids is: (+)Cedrol>(+)Carvone>(-)Carvyl acetate>(-)Carveol>(-)Menthone. Furthermore, when the concentrations of (-)Carveol, (+)Carvone, (-)Menthone, (-)Carvyl acetate and (+)Cedrol are respectively 0.033 mmol·L^-1, 0.030 mmol·L^-1, 0.080 mmol·L^-1, 0.020 mmol·L^-1 and 0.001 mmol·L^-1, inhibition rate could theoretically reach 93.69%.