To improve the reliability effectively, the reliability sensitivity method is researched with considering that a mechanical system or component may fail in many modes, which is simplified to be a series system model. It is supposed that all ultimate state functions in multi-failure modes are normal distribution. A computation module for total reliability is established. A kind of computation method for reliability sensitivity in multi-failure modes is built based on that in single failure mode. A pin connection component that may fail in shear fracture, bruise on pin or hole surfaces, or in any assemble with two different modes is computed, and the reliability and sensitivity of the component are estimated. Consequently, it is found that the most effective method to enhance the reliability was to enhance the crushing strength of the pin.