In order to meet the requirements of thermal damage assessment of large equivalent warhead, improve the impact and ablation resistance of the traditional thin-skin calorimeter, a new type of heat sink cooling heat flux sensor is designed by adding heat sink to the rear surface of heat sensitive element. The incident heat flux can be indirectly obtained by measuring the rear surface temperature of heat sensitive element. In this paper, the model of sensor is established, the response time expression is derived, and the response characteristics of the sensor are simulated by numerical simulation. Simulation results show that: The response time of sensor is only related to the size and material of heat sensitive element, and not related to the heat sink. The response time of sensor which designed with the copper heat sensitive element is about 1.1ms; Greater the endothermic coefficient of heat sink is, smaller the temperature rise of heat sensitive element becomes. At the same time, the temperature rise rate decreases gradually with the increase of time. Validation experiment shows that the addition of heat sink can effectively reduce the temperature rise of heat sensitive element, and the sensor can correctly reflect the change of incident heat flux.