Abstract: As a typical strong discontinuity, tensile soil crack is a popular failure mode in geotechnical engineering. In recent years, such failure problems are usually solved using an extended finite element method (XFEM) due to its flexibility and compatibility, but its application to three-dimensional tensile soil failure is lacking. Besides geometrical complexity, the 3D applications also meet the difficulty of determining the developing direction of the front. This paper describes a crack tracking algorithm that can be integrated into a XFEM code, and presents a scheme of integrating crack planes for rather accurate and convenient simulations of 3D tensile failure. We first review the theoretical basis for XFEM, then discuss implementation of this new algorithm and describe a geometric treatment and quadrature scheme for crack interface calculation, and finally present simulations of a cross cracking process in the core wall of an earth-rockfill dam to demonstrate the efficiency of our new algorithm.