Abstract: In order to probe the allelopathic from leaves and husks of Carya illinoensis, the effects of different concentrations (0.005, 0.01, and 0.1 g·mL-1) of water extractions from leaves and husks of C. illinoensis on the seeds and plants of Triticum aestivum, Brassica napus, and Vigna radiata were studied with indoor bio-assay. The results showed that water extractions improved seed germination plant height of tested plants in low levels (0.005 g·mL-1), whereas inhibited in high levels (0.1 g·mL-1). Some plants showed improved or inhibited effect within the scope of its concentration, but with the increase of concentration they also performed the promoting effect to reduce or inhibition enhance. The inhibitory effect of water extractions from leaves and husks of C. illinoensis on root length was higher than on shoot height for 3 crop species, but had different impacts on the fresh and dry weight of receptors due to variant species. The order of the synthesis effects of water extractions from leaves of C. illinoensis on 3 plant species is T. aestivum > V. radiata > B. napus. The order of the synthesis effects of water extractions from husks of C. illinoensis on 3 plant species is T. aestivum > B. napus > V. radiata. To synthesize the allelopathic effect of 3 plant species, the promoting effect of water extractions from leaves of C. Illinoensis on 3 plant species is higher, but the inhibition of water extractions from husks of C. illinoensis on 3 plant species is higher in the same concentration.