A cable-driven parallel manipulator is an economic way to achieve manipulation over large workspace. However, unavoidable vibration in long cables can dramatically degenerate the positioning performance of manipulators. In this paper, dynamic models of large cable-driven parallel manipulators (CDPMs) are addressed where each cable is considered with distributed mass and can change in length during operation. The dynamic equation of a cable deployed or retrieved is derived using Hamilton's principle. The dynamic model of the system is characterized by partial differential equations with algebraic constraints. By properly selecting the independent unknowns, we solve the model using assumed-mode method.