This paper introduces the architecture and working principle of the magnet-less bulk acoustic wave (BAW) circulator, which consists of three identical MEMS bulk acoustic wave resonators (BAWRs) and spatiotemporal modulation (STM) circuit based on varactors connected in wye configuration. In order to be able to predict the performance of the BAW circulator accurately, we present a hybrid frequency-time domain simulation analysis method. First, the MBVD model of BAWR and circuit simulation model of BAW circulator are respectively established. And then, the harmonic balance method is used to simulate scattering properties of BAW circulator. Meanwhile, the influence of modulation signal amplitude on performance of circulator is analyzed and the optimal modulation condition is determined. Finally, BAW circulator case at 1.805 GHz is designed by this method. The simulation results show that insertion loss is less than 3.6 dB, and isolation is greater than 14 dB.