LEO satellite constellation-based IoT is a novel direction, providing an optimal solution for terrestrial IoT system. LEO satellite communication has advantages of low propagation delay, small propagation loss and global coverage. Existing IoT technology is not suitable for satellite IoT scenarios, this paper will introduce a novel protocol design for LEO satellite constellation-based IoT. We adopt the technology of spread spectrum Aloha in reverse link to reduces the complexity of the protocol, design channel mapping for the limit wireless resource, simplify the procedure of authentication and random access for the purpose of reducing signaling interactions. The protocol will be described in the aspects of network architecture, radio protocol stack architecture, and random access procedure. In addition, we have implement a basically available simulation platform based on NS3 for research the protocol design.