Beetle antennae search (BAS) is an efficient meta-heuristic algorithm. However, the convergent results of BAS rely heavily on the random beetle direction in every iterations. More specifically, different random seeds may cause different optimized results. Besides, the step-size update algorithm of BAS cannot guarantee objective become smaller in iterative process. In order to solve these problems, this paper proposes Beetle Swarm Antennae Search Algorithm (BSAS) which combines swarm intelligence algorithm with feedback-based step-size update strategy. BSAS employs k beetles to find more optimal position in each moving rather than one beetle. The step-size updates only when k beetles return without better choices. Experiments are carried out on building system identification. The results reveal the efficacy of the BSAS algorithm to avoid influence of random direction of Beetle. In addition, the estimation errors decrease as the beetles number goes up.