A systematic theory of reliability is based on probability theory. It is well known that the conventional reliability analysis using the probabilities has been found to be inadequate to handle the uncertainty of failure in data and modeling. The fuzzy set theory provides an useful tool to complement conventional reliability theories. This paper proposes the transmission flow system design in series-parallel structure to evaluate the maximum reliability subject to the system cost. The co-efficient of variation (CV) is introduced to estimate each membership function. This approach is to find minimum CV with high reliability estimate. © Research India Publications.