In this paper, three kinds of soft chain motions are solved by using the momentum theorem of particle system, and their respective characteristics are revealed. At the same time, it is shown that the advantages of the method of momentum theorem lie in the protruding physical thought and the concise calculation process. The specific characteristics of the third motion are analyzed and calculated step by step by iterative method, and the main motion characteristic parameters are used to describe the successive attenuation oscillation of the chain. The necessary diagrams, demonstrations and explanations are given, and some regularity are found. In addition, a practical so-called “dynamic equation of tangential motion of chain particle system” is proposed.