The present disclosure describes a heater of heat storage agent and a Brayton solar thermal power unit with heat storage. The Brayton solar thermal power unit with heat storage may include: a heat storage agent flow adjusting module, a solar energy collecting module, a heater of heat storage agent, a heat exchange module, a thermal power generating module a heat storage agent transporting module. The heat storage agent flow adjusting module may be connected with the heat storage agent transporting module and the heater. The heater may be connected with the solar power collecting module, and the heat exchange module. The heat exchange module may be connected with the thermal power generating module and the heat storage agent transporting module. The present disclosure can significantly increase maximum power capacity of Brayton solar thermal power unit to megawatt level, improve operation efficiency, and avoid discontinuity and instability of solar power generation.