The stability of a landfill is a key issue for the safety of the landfill project. Thus, centrifuge test and numerical simulation were carried out to investigate the stability of vertically extended earth dams in landfill projects. The stability of a steep extended earth dam with or without reinforced by geotextile was studied through centrifuge test, and the rationality of the design was verified. Before using the finite element (FE) method for parametric study, the FE model was validated by comparing with centrifuge test data in terms of soil displacement. Then, numerical simulations were conducted to extend the centrifuge test data during construction and operation stages. For extended earth dam reinforced by geotexile, the safety factor of the dam and the position and shape of potential slip surface were investigated under different working conditions during construction and operation stages. Effects of parameters such as permeability of fill soil, reinforced methods, shear strength of fill soil, stiffness and arrangement of reinforcement were analyzed and compared. Results show that for vertically extended earth dam projects, the stability of the steep dam reinforced by geotextile was effectively improved and not constrained by site conditions, which meets the demand of safety for design purpose.