Reliability of equipment has long been considered as an important quality characteristic. But the reliability assessment of multi-parameter system still remains a problem. Based on the multi-parameter degradation process of a certain diesel engine, the article proposes a reliability assessing method for multi-parameter degradation system. The method uses SVDD to convert multi-parameter into one single degradation measure which reveals the overall system degradation. Using degradation measure distribution, a reliability assessment model is built. Through experiments on vehicle, the method shows the degradation regular of vehicle diesel engine, builds the reliability curve, provides evidences for equipment maintenance.