The next-generation vehicular network will see an unprecedented amount of data exchanged which is beyond the capacity of existing communication technologies for vehicular network. The much talked millimeter-wave (mmWave)-enabled communication technology is the potential candidate to this growing demand of ultra-high data transmission and related services. However, the unfavorable signal characteristics of mmWave bands make the quality of service guarantee more difficult when it is applied to user mobility. In this paper, we proposed a directional beam-based power allocation/re-allocation scheme to guarantee the quality of service (QoS) in a high user mobility scenario operating on mmWave band. The performed simulation results show that our proposed scheme outperformed the baseline scheme without power allocation. © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021