A dynamics modeling for endless-track vehicle is established in this paper. Endless-track vehicle is simplified as three part rigid body systems: bodywork and two sides pedrail system. The pedrail system is reduced flexible cable constraint and the mathematical description of flexible cable constraint is descripted by skate add wheel mode. A dynamics modeling for endless-track vehicle is established through using multi rigid body system theory. The result indicates that skate add wheel mode′s mathematical description belong to one order linear nonholonomic constraint. A dynamics modeling for endless-track vehicle is created by Routh eqeation.