Reliability is a parameter of evaluating network performance and expected path length can index the contribution of s-t paths to network reliability. It is meaningful to observe the important part of network performance in light of the reliability and path length. In this paper, we attempt to reveal the important part of network performance based on reliability. Conversely we consider the optimization problem of two-terminal reliability with expected-path length constraint. Next, we transform the problem into searching delta-maximum graph, in which its expected path length is not greater than delta(0) and reliability is maximum. Further, we find a rule of removing redundant subgraphs and propose an algorithm to search the optimal solution. Simulation shows the effectiveness of the proposed algorithm.