The present invention provides a system using label switching techniques to support QoS for mobile ad-hoc networks and its label distributing and switching method. The system includes plural clusters, each having plural mobile nodes. At least one mobile node in a cluster is selected as a routing agent. One routing agent in a cluster is selected as a core routing agent. Each core routing agent is capable of obtaining an unique seed for generating an label L=f(S, i, j)=S×3i×2j to a new LSP, where S is an unique seed that is an unique prime number, except 2 and 3, obtained by the core routing agent, i represents one of different kinds of LSP, and j represents one of different numbers for the same kind of LSP. Through the interconnecting of core routing agents, the virtual backbones can be constructed for bandwidth sharing.