Abstract: Based on the theory and calculation method of elastic foundation beam,the control differential equation of tunnel lining is worked out.According to the Saint-Venant theory,the predominance equation of the center angle to the crack space is established,and then the crack space of tunnel lining can be worked out under the unfavorable loads.According to the crack space,the crack width can be calculated under the conditions of the same and different crack space,and according to the engineering example,the calculation of crack parameter is more acceptable.