Abstract: Nuclear Reactor Coolant Pumps Group（NRCPG） is a complex redundancy system which contains more than one common causes and multiple common cause component groups（CCCG）,and it is complex and difficult to conduct the uncertainty analysis for the system failure probability.In this paper,GO-FLOW combined with Monte-Carlo is applied to solve this problem,and the uncertainty of the system failure probability considering the common cause failure（CCF） is quantitatively calculated.The results show that the mean value of system failure probability is obviously increased by CCF,and the occurrence of the multiple common cause failure makes the standard deviation,x₀₅ and x₉₅ which contain 90% range of uncertainties larger,but makes the error factor E_F smaller;The probability density function（PDF） curve of the system failure probability describes the integrated distribution,so it can make up the imperfection caused by the point estimate value used to evaluate the system reliability.