This paper investigates the Lie symmetries and Noether conserved quantities of discrete non-conservative mechanical systems.The variational principle of discrete mechanics,from which discrete motion equations of systems are deduced,is generalized to the case of including the time variational.The requirement for an invariant group transformation is defined to be the Lie symmetry and the criterion when the Noether conserved quantities may be obtained from Lie symmetries is also presented.An example is discussed for applications of the results.