The paper analyzed the strengthening mechanism of plant root from the perspective of composite materials.The rock and soil with plant roots was regarded as a special composite material.The rock and soil was basal materials

and plant root was the reinforcement materials.Root like fiber played a cracking resistance and enhancement role in the composite of root and soil.By Using energy principle to study root’s cracking resistance and enhancement action

a calculating formula of shear strength increment of one point in the composite of root and soil was educed

and the formulas of root’s resistance pull-out risistance and maximum pull-out length in the point too.A theory is established that the shear strength increment of one point mainly relates to root’s area ratio

areal density

the ratio of length and diameter

tensile strength and the cohesion and friction coefficient between the roots and soil.Thus the conclusion is drawn that if the anchor length of root deep into one point is greater than the maximum pull-out length of the root in the point

the root would break.