In order to solve the problems of complexity increase and restoration difficulty in qualitative and quantitative analysis of common cause failure by traditional dynamic fault tree, this paper proposes an extended fault tree, which simulates common cause failure through common cause failure transfer operator and common cause failure pattern tree to optimize Fault tree analysis under common cause failure. Then, a new discrete time Markov analysis method was proposed by combining the Semi-Markov universal model. Finally, by modeling and analyzing a wheel brake system, an extended fault tree is established and reliability analysis is conducted on the extended fault tree. Practice has proven that this method can improve the modeling and analysis efficiency of reliability analysis methods for common cause failures, providing new ideas for common cause failure analysis.