This paper presents a sensitivity analysis method that provides a powerful tool for understanding the behavior of large and complex systems. This method produces easy-to-understand results that can explain the performance of a system clearly at the component level rather than parameter by parameter. A system model for the proposed disposal of high-level radioactive waste at a potential geologic repository at Yucca Mountain, Nevada is used as an example to illustrate the use of the method. The component sensitivity analysis, together with parametric sensitivity analysis, can produce a more complete picture of system behavior.