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The main mechanical properties of wheat stems in maturity were tested by the electronic testing machine CMT2502. The content of chemical compositions of cellulose, hemicelluloses, lignin, protein, lipid and total carbohydrates of wheat stems in different conditions was determined, and the relation between mechanical properties and major chemical compositions in wheat stems has been analyzed. The results show that the maximum tensile force, tensile strength and Young's modulus of wheat stems are 182.38～242.74N, 30.36～52.65MPa and 1143.44～1985.86MPa respectively; the content of cellulose, hemicelluloses and lignin of wheat stems are 22.58～48.18 percent, 10.85～22.45 percent and 4.83～10.59 percent respectively. A wheat stem is a natural anisotropic polymeric composite consisting of cellulose, hemicelluloses and lignin. The strength, stiffness and elasticity of wheat stems mainly depend on the content, linking form and sequence of cellulose, hemicelluloses and lignin.