For more degree of freedom, complex topology and high coupling between base and manipulator, the kinematics and dynamics of large free-floating branching robot system are difficult to analyse. A free-floating branching robot system was researched by dividing into two parts, ground robot of fixed base and locking joint robot of floating base. Then it can avoid the analysis of the coupling between base and manipulator,so the Jacobian matrix can be achieved simple and efficiency. And the computional efficiency is improved by the methods of combining screw and recursive operator, which is the foundation of the dynamics.