The traditional loading-strength interference model is used to calculate the reliability of components and system when random loading act once. In fact, components always work under repeated random loading, so it is important to derive a reliability model considering the frequency of loading. The two-dimensional distribution of random loading is proposed in this paper. In engineering practice, only a few samples of time-loading process can be obtained because of all kinds of limitation, so the reliability model based on transverse distribution of random loading. In addition, when it is difficult to know the exact distribution of random loading and strength, a discrete reliablity model is developed through the method of universal generating function. Finally, the reliability of system is analyzed considering common cause failure.