Abstract: There are some flexibility and uncertainty in the root of a cantilever with bolt joints. The dynamic equation and the approximate result of the cantilever with flexible parameters are presented in the paper. At the same time, in order to study the uncertainty modeling, the translation and rotation flexible parameters are chosen as the uncertain parameters. Then the flexible parameters are identified according to some modal test results. The mean and standard deviations of flexible parameters are obtained by analyzing the identified results subjected to the normal distribution assumption. The mathematical models of the uncertain parameters varying with the pre-torque are built. The models are validated by other modal test results, and the applicable ranges of the models are obtained according to the results.