In this paper,a series of direct shear tests were carried out on cultivated ryegrass-reinforced undisturbed clay,the effects of root content and water content on shear strength properties of reinforced clay were studied comparatively,and the mechanism was analyzed according to the research results. The test results show that with the increase of root content,the shear strength and cohesion of reinforced soil gradually increase,and the change of internal friction angle is slight. This is induced by the presence of roots which strengthen the friction between soil particles. Moreover,the root elastic deformation occurs in the process of shearing,and the internal tension stress of root is transformed into the force that resists the displacement of soil by friction. It is therefore the strength of soil is enhanced. With the increase of water content,the shear strength and cohesion of the reinforced soil decrease,and the internal friction angle changes little. This can be attributed to that,on the one hand,the presence of water reduces the pull-out resistance of roots and the friction resistance between soil particles,and on the other hand,the increase of water content leads to a decrease of matrix suction,which reduces the strength of liquid bridge between soil particles,thus reducing the shear strength of soil.