The variation rules of strength, load and reliability of mechanical components were studied with the change of time, and a model for dynamic reliability of mechanical components was established under the random load acting. According to the model, the design of dynamic reliability sensitivity was discussed as well as the approach to calculate dynamic reliability sensitivity was proposed, meanwhile, combining the theory of reliability-based optimization design with the method of sensitivity analysis, the computation model of dynamic reliability-based robust optimization design was established, then the problem of dynamic reliability-based robust optimization design of mechanical components is solved.