The clustering scheme is used to configuring Ad Hoc networks, so the performance of this structure needs to evaluate specially for reliability. In order to solve the problem on s-t reliability of clustered Ad hoc networks, a new formula is proposed in this paper. Based on certain clustering algorithm, a concept of breviary graph is presented to divide the computing process into intercluster and intracluster. Then the result can be calculated with the probability of the product of independent events. In addition, integrating the concept of normalized capacity weight, the reliability of clustered Ad Hoc networks is combined with variable linkcapacity. Finally, a practical simulation proves that it can be implemented by computer.