Summary: A cold standby repairable system consisting of two identical components and one repairman is studied. Assume that each component after repair is not "as good as new", by using a geometric process, we consider two kinds of repair replacement policy, one based on the working age $T$ of component 1 under which the system is replaced when the working age of component 1 reaches $T$, and the other based on the failure number $N$ of component 1 under which the system is replaced when the failure number of component 1 reaches $N$. Our problem is to choose optimal replacement policies $T^*$ and $N^*$ respectively such that the long-run average cost per unit time of the system is minimized. And we can prove under some mild conditions that the optimal policy $N^*$ is better than the optimal policy $T^*$. Finally, a numerical example for policy $N$ is given.