Using thermostatically controlled load (TCL) as a frequency regulation resource is an effective means of maintaining power grid frequency stability caused by the high proportion integration of renewable energy power generation into the power grid. A primary frequency control strategy is proposed for the participation of TCL in regulation based on dynamic droop control. The dynamic droop control model is constructed to control the participation of TCL aggregators in frequency regulation by adjusting the droop control coefficient in real time, while considering the average state of temperature of TCL, the capacity for frequency regulation and the rate of change of system frequency. In this condition, the off state of TCL is locked for regulation up, vice versa the on state is locked for regulation downward. Therefore, the frequency can quickly return near its rated value. At the same time, to ensure the user's comfort, the priority ranking list dispatch method on the state of temperature is used to determine the order of TCL for frequency regulation. Finally, simulations on the Matlab/Simulink platform show the effectiveness of the proposed strategy in improving frequency quality and the user's comfort.