Abstract: To analyze the expansion of the cylindrical cavity in loess,a reasonable numerical model was presented based on field investigation.The potential function theory and Laplace transform technique wwere used to solve the problem.The analytical solution of stresses,pore pressure and displacement induced by inner water pressure were derived in Laplace transform domain.Numerical results were obtained by inverse Laplace transformation.The effects of rainfall duration and saturation on dynamic response of the cavity were discussed.It shows that the hydrodynamic force is the key factor of the cavity expansion in loess.The rainfall duration has great effects on the stress and displacement. The influence of saturation on displacements is remarkable.