Constructing a disjoint minimal path set is an important approach for the reliability analysis of networks. Based on the disjoint theory and the BDD algorithm, an improved algorithm is presented for directly and simplily constructing disjointed minimal paths in which different disjoint methods are used for the minimal path set with different path lengths. According to the improved algorithm, a program is provided to obtian the disjointed minimal path set of the network system,and network reliability can be effectively worked out.Finally, a numerical example is given. It is shown that the method is efficient and accurate. It provides a new approach for the reliability analysis of largescale network systems.