Disclosed are a reliability evaluation system for multi-state flow network and a method thereof. The system includes an element-gaining module and a reliability calculation module. The method includes using a GCF calculating means to calculate an initial reliability according a first and second system-state vector, comparing values of all elements in a set being composed of elements of a second grade of a third system-state vector, excluding an element with a greater value and other related thereof in all grades in the third system-state vector when only one element in the set except the element with greater values so as to obtain remaining elements, using the GCF calculating means to perform the calculation of the remaining element to obtain a calculation results, and summing the initial reliability and the calculation results so as to obtain a reliability of the multi-state flow network. |