The invention discloses a device for participation of photo-thermal power generation in primary frequency modulation of a power grid and a control system and a method. According to the system, a photo-thermal power generation system is additionally arranged in an existing power generation device, so that when a unit stably runs, the photo-thermal power generation system generates power according to a power grid load instruction; and when the load is lower than system output work, redundant heat is stored. When the load fluctuates and the power grid frequency fluctuates, under the action of thecontrol system and the execution mechanism, heat storage in the heat storage tank and the pipeline is input or withdrawn in time, and the primary frequency modulation capability of the system is sequentially improved.