Abstract: This paper introduces the safety integrity level verification and analyzes the dangerous failure factors of the considered system.By using MBF parameter model,this paper quantitatively calculates the probability of common cause failure of the system.Moreover,the impact of independent failure probability for the safety instrument system is analyzed.Finally,the application example shows that the proposed method is not only closer to the actual redundant structure of safety instrument system in the industrial production,but also greatly simplifies the calculation and deals with the shortcoming of Markov model with complicated calculating procedure.