For the characteristics of high dynamic, large scale, sparse nodes distribution, diversity of communication traffic, etc., and the high reliability and low latency of information transmissions in airborne tactical networks, a multi-channel slotted-ALOHA (MC-S-ALOHA) protocol is proposed. The protocol adopts a backoff mechanism based on the number of active nodes, whose size of the contention window is adjusted adaptively and dynamically with the number of active nodes in the network. For the proposed protocol, by establishing the two-dimensional Markov chain model on the number of busy channels and active nodes, and the one-dimensional Markov chain model on the sending buffer of nodes, the mathematical expressions of network throughput, packet end-to-end delay and packet success probability are derived. The simulation results verify the accuracy of the theoretical derivation, and show that the protocol can meet the performance requirements of airborne tactical networks.