In general, depots of transit systems include primary depots and secondary ones. This project constructed the location models of primary and secondary depots separately to minimize the total cost subject to train assignment and depot capacity. The "decision rule" approach is applied to solve these models. This method compares the benefits by three stages in sequence to determine whether each of the candidate locations is selected or not. These models were applied to the Taipei Rapid Transit Systems. Computational results show that the optimal solution is superior to the existing locations.