This paper deals with a discrete-time Geo/Geo/1 working vacations queue with negative customers and N-policy control in which the positive customers arrive at the system in different input rates during the working vacation period and the normal busy period.  Employing the quasi birth-death process and the matrix-geometric solution method, we derive the steady-state queue length distribution and the expected queue length, as well as the steady-state probabilities that the system is in working vacation state and busy state. Meanwhile, the busy period and the application for the steady state queue length distribution in system capacity optimum design are discussed. Finally, through numerical calculation, it is determined the optimal control policy N* such that the long-run expected cost rate is minimum under a given cost structure.