A cold standby repairable system with preventive repair is studied. The system consists of two dissimilar components. Component 1 is the main component with use and repair priorities, while component 2 is the supplementary component. Assuming the failure repair of the main component follows an extended Poisson process, preventive repair for the main component is performed every time interval T and is ″as good as new″. The successive working time and the repair time of the main component after failure form two extended Poisson processes. While the repair for component 2 is also ″as good as new″. The working time and the repair time of component 2 are both exponentially distributed. By the renewal reward theory, the explicit expression of the expected cost rate is derived. Finally, an example is given to illustrate the theoretical results for the proposed model.