Abstract: In this paper according to the results of a great quantity of tests and numerical calculations, it is pointed out that the country rock with thickness of 1/3 span has mechanical characteristics of a thick flexure member in underground rock cave subjected to transverse blast loading, however, it is approaching to stress state of free ffield outside country rock, the equation of thick plate theory under loading of free field pressure may be applicable to solution of this problem.Therefore, the underground structure-cuuntry rock dynamic interaction may be described by dynamic equations of flexure member of thin plate and thick plate, which express liner and country rock respectively.The interaetion force between the liner and country rock is expressed as contacting pressure function q(x,t),Solving the system of simultaneous equations, the analytical solution to riynamic analysis of arch-straight liner including elastic half space interaction effect is given and the analytical expression of function q(x,t) is obtained.This analytic solution will be contributed to the study of some substantive problems of underground structure-medium interaction.