Abstract: The continuous drainage boundary can correct the pervious and impervious boundaries which are extremely idealized. Based on the Terzaghi’s one-dimensional consolidation theory and the continuous drainage boundary; an analytical solution of one-dimensional consolidation of undrained symmetry plane under continuous drainage boundary is given. One-dimensional subroutine of continuous drainage boundary is written based on the finite element analysis of ABAQUS. The influence factors of undrained symmetry plane is studied; including boundary permeability; drainage time and permeability coefficient. The variation of the undrained symmetry plane is obtained. Finally; the location of setting sand layers at different depths in saturated soft clay is compared by the method of finite element analysis. The results show that the rate of consolidation is the fastest when the sand layer is set at the location of undrained symmetry plane. The continuous drainage boundary can help to determine the location of undrained symmetry plane. The results and the process of finite element analysis are of practical and important value and significance for the development of soil consolidation theory.