Abstract: Maize straw residue was decomposed under laboratory conditions, and filtered at different time. The decomposed liquid was tested for bioassay. It was found that the inhibitory effects of maize straw decomposed liquid on height of wheat seedling, dry weight of stem and leaf were strong when the concentration of decomposed liquid was high. All concentrations of decomposed liquid suppressed the germination of wheat seeds and dry weight of root. Root activity in TTC reduction of wheat became low when the concentration of decomposed liquid arranged from low to high. The maize straw decomposed liquid filtered at different time showed inhibition to the pathogens of Rhizoctonia cereali Vander Hoeven, Gaeumannomyces graminis (Sacc.) Arxer Oliver, Bipolaris sorokiniana (Sacc.) Shoem. to some degree.