Experiments were performed on a ring-on-disk tribometer under lubricated conditions. Friction force was measured throughout the friction process. The parameter predictability was used to provide a quantitative description of the intrinsic randomness of the friction force. The parameter dynamic difference was used to detect the dynamic abrupt changes. The results show that, from the perspective of dynamics, the friction process can be divided into the abrupt changing process through which the intrinsic randomness is enhanced, the dynamic stable process through which the system maintains the strong intrinsic randomness, and the abrupt changing process through which the intrinsic randomness is weakened.