The invention discloses a space-based backbone dynamic access system, node, management center and method. The dynamic access system comprises user nodes and an inter-satellite network management center; each node transmits a service request to the inter-satellite network management center by using a self-installed Beidou message terminal; the inter-satellite network management center receives andprocesses the transmission service request by using the self-installed Beidou message terminal, and accomplishes the data transmission planning of the space-based backbone network, thereby enabling the user to dynamically and randomly access to the space-based backbone network. By using the dynamic access system disclosed by the invention, the dynamic random access of the user node can be realized, the data transmission request of the user node can be responded in real-time or near real-time.