Slot-ALOHA is widely used in wireless communications due to its simplicity. However, because slot-ALOHA is not stable in essence, many algorithms have been used to provide steady throughput. After founding the Markov model for Binary Exponent Backoff (BEB) algorithm, this paper analyzed the adjusting progress. The numerical computation and simulation results demonstrate that BEB algorithm can guarantee the system steady and the theoretic throughput can be derived when the number of modes is within certain range. By comparing throughput of BEB to that of Pseudo-Bayesian Control Algorithm (PBCA), it can derive that the throughput of BEB is less than PBCA when the number of users is either too big or small because of being influenced by the backoff window size.