Sensitivity coefficients are commonly used in the analysis of the influence of various uncertain factors on the reliability of dam structures; however, the values of the sensitivity coefficients are selected from the range of the local design checking points. In order to overcome the defect of locality, the global importance analysis method of the factors which can influence the dam structural reliability is studied for the analysis. Firstly, on the basis of the dam structural reliability analysis model, the global importance measurement index of influencing factors are determined considering the changes of uncertain factors in the whole failure domain. Then, Monte Carlo simulation combined with truncated importance sampling(TIS-MCS) is used to quantitatively calculate the global importance measurement index. Finally, the structural reliability analysis model of a dam is established to calculate and compare the global importance measurement indexes and sensitivity coefficients of the uncertain factors. The result shows that the global importance measurement index can reflect the influence of uncertain factors on the dam structural reliability more comprehensively than the sensitivity coefficient.