Using Arabidopsis thaliana as material, we studied the allelopathy potential of the diterpene compound oridonin on the seed germination, growth and physiological reaction of A. thaliana seedlings. The results showed that:（1） oridonin treatment reduced A. thaliana seed germination rate, germination potential, germination index and seed vigor index; until the final germination time, the germination rate, germination potential and germination index were 87.76%, 70.37% and 83.19%, respectively in 120 μmol/L oridonin treatment, the seed vigor index was only 27.72% of the control. It showed that oridonin in higher concentration had significant inhibitory effects on the seed germination rate, germination potential, germination index and seed vigor index. （2）After two weeks culture, the lateral roots were inhibited totally in 60 μmol/L oridonin treatment. And the seedling primary root lengths decreased by 79.05%, while the fresh weights, dry weights and relative water contents were reduced to 58.41%, 63.33% and 93.91%, respectively in 120 μmol/L oridonin treatment. （3）The accumulation of osmotic regulators, soluble proteins and proline in A. thaliana seedlings were also overall promoted by oridonin at different concentrations and treating time. The study presented here confirmed that oridonin had inhibitory effect on seed germination and seedling growth of A. thaliana. And this allelopathy effect was closely related with both oridonin concentration and treatment time; Arabidopsis thaliana seedlings could alleviate this inhibition to a certain extent by increasing the accumulation of their own osmotic adjustment substances.