Abstract: A risk analysis method based on Bieniawskis RMR system was proposed. Firstly, variables which were acquired for the RMR classification system were obtained from field and laboratory investigation of the core samples . Secondly, distribution functions and parameters of all variables are determined using statistic method. Thirdly, 20000 RMR values have been obtained utilizing Monte Carlo method and the results are plotted . Finally, risk analysis can be made from above results. This method acquire good results in applied to the research on quality of rock masses in Runyang Yangze River Highway Bridge Project .