Abstract: This paper presents a new method for the reliability analysis of multi-stage production lines with unreliable machines and finite buffers, based on the modeling of probabilistic flow. First, a new concept-production balance ratio is introduced, and the related equations are derived. Second, the system state equations are solved analytically. The computational burden is reduced and the computing precision of the reliability index is increased. Then, the reliability formulae of system throughput, availability, mean sojorn time and mean inventory are derived. Finally, some examples are given to show the effectiveness of the proposed method.