In this study, dynamic behavior of a mooring line in a floating system is analyzed by probability approaches. In dynamics, most researches have shown the system model and environments by mathematical expression. We called this process as the forward dynamics. However, there is a limit to define the exact environments because of uncertainty. To consider uncertainty, we introduce the redundancy in flexible system, mooring line. For verifying the effectiveness and stability of the mooring line, criterion of axial breaking load of the mooring line is applied to joint reaction forces according to the various path of the mooring line. To cover the limits for defining the non-linearity of the environments, various responses of the mooring line along the redundancy that is used in Robotics, are derived by probability distribution. By using the Newton-Euler formulation, the inverse kinematics and the linear acceleration theorem to get joint displacements, velocities and accelerations, the joint reaction forces and moments are calculated and probability distribution of the mooring about stability and compatibility is investigated. Lastly, we simulate the flexible systems in various null motions, calculated each joint torque and force, and evaluated failure probabilities using the Monte-Carlo method.