Abstract: In order to illustrate the physiological mechanism of weed suppression ability of allelopathic wheat (Triticum aestivum L.), two strong allelopathic wheat accessions ('115/Qinghai' and '92L89') and one weak allelopathic accession ('Kang10103') were used in hydroponic culture experiments. Alopecurus aequalis seedlings were cultured in the hydroponic culture solutions with 0.2%, 0.5% and 1.0% of roots water extracts of the above three wheat accessions. The fresh weights, contents of chlorophyll (SPAD value), soluble proteins, methane dicarboxylic aldehyde (MDA), flavonoids, total phenols and the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) of A. aequalis seedlings were determined after cultured for 21 days. The results showed significant differences in weed suppression ability among wheat accessions and concentrations of roots water extracts. Strong allelopathic wheat accessions had higher inhibitory rates to A. aequalis seedlings than weak allelopathic wheat accessions. The inhibitory rate to A. aequalis seedling fresh weight of different wheat root water extracts within designed concentrations was in the order of '115/Qinghai' (24.7%-74.3%) > '92L89' (15.7%-71.6%) > 'Kang10103' (13.8%-61.4%). Wheat accessions with extract concentrations of 0.2%, 1.0% and 5.0% had inhibitory rates of 13.8%-24.7%, 41.7%-66.4% and 61.4%-74.2%, respectively. The contents of chlorophyll decreased with increasing extract concentration while the contents of soluble protein, MDA, flavonoids, and activities of SOD, POD and CAT increased with decreasing extract concentration. Strong allelopathic wheat accessions had higher stimulation effects on physiological indexes than weak wheat accessions. In addition, total phenol content of A. aequalis seedling treated with 1.0% water extract of '115/Qinghai' wheat and 5.0% water extracts of the three wheat accessions were higher than the control. Thus allelopathy effects of wheat root water extracts enhanced enzyme activities, stimulated metabolism of anti-oxidatives, accompanied stronger lipid peroxidation, degraded leaf chlorophyll and inhibited growth of A. aequalis seedling.