Abstract：The dynamic response of a spatial flexible beam undergoing large overall motion with tip mass and uncertain parameters was investigated. using the assumed modes method and the Lagrange’s equations, the first-order approach coupling stochastic dynamic equations of the spatial flexible beam carrying a tip mass were derived．The polynomial chaos method and a regression-based collocation method were applied to derive a set of completely implicit differential equations. The resulting system of deterministic equations was then solved to find the numerical characteristics of the response. As an illustrating example, dynamic modeling of a spatial flexible beam considering the probabilistic of geometric and physical parameters was presented. Simulation results demonstrate that probabilistic parameters have a significant effect on the dynamic response of the flexible beam and the dynamic modeling with probabilistic parameters can objectively reflect the dynamic behavior of the objective systems.