Aiming at the problem of large profile of commonly used time-domain end-fire antennas, this paper designs a low-profile directional bow-tie antenna in the time domain by using the method of adding a reflector. The method of making an omnidirectional antenna directional in the time domain is described in detail. The method is applicable to all omnidirectional antennas. Defining the time-domain directivity as the ratio of the antenna forward-radiating pulse amplitude to the backward-radiating pulse amplitude, the directional butterfly antenna has a time-domain directivity of 3.22, which is greatly improved compared to the conventional bow-tie antenna.