A system of evaluating the reliability of deterioration-effect multi-state flow network and method thereof are disclosed in present invention. The system can evaluate the probability that d units of data of flow can be transmitted from a source node to a sink node. In practical application, the flow in a deterioration-effect multi-state flow network may undergo a loss due to deterioration. For example, electrical power will decrease if the transmission distance is too great. Therefore, how to evaluate the reliability of deterioration-effect multi-state flow network becomes an important issue.