Abstract: Transportation equipment is a reliable guarantee of performing fast rescue. These equipments, whose cumulative failure numbers increases with age and mileage increasing, are degradation systems. Within a given time, the cumulative failure number is a random variable. And failure severity is very different. This paper classifies all failures into three categories according to two factors, the downtime, and repair cost. Then the maintenance optimization model is built. Finally, an empirical case is used to illustrate the effectiveness of the proposed method.