To improve the accuracy of human thermal injury assessment and protect rescuers' safety in thermal radiation environments，a coupled heat and mass transfer model of skin-microenvironment-firefighting clothing system was proposed to predict skin burn injuries under dynamic conditions. Based on mechanism of heat and moisture transfer in porous media，the periodic movement of fabric caused by human activities and its impact on heat and mass transfer in the skin-microenvironment-firefighting clothing system were considered. Furthermore，the proposed model was used to simulate skin temperature，time of skin burn，and the distribution of temperature and humidity in the fabric layers for both dry and wet cases in real time. The results show that the relative error between simulated values predicted by the model and the experimental measurements presented in the literature is only 3.79%. When exposed to 8.5 kW/m² thermal radiation environments，the time to second-degree burn for the dry case is 33.7 s earlier than that for the wet case. When firefighters approach a 20 kW/m² radiant heat source at a speed of 1 m/s，the heat transferred is impeded by the increase in thermal layer thickness. This extends the time for second-degree burns to occur by 10.9 s and reduces the heat absorbed by the skin surface by 20%. When the air gap thickness in the microenvironment is the same as the amplitude of the periodic motion of fabric，the skin temperature increases rapidly and fluctuates significantly，and the time to second-degree burn occurs 43.7 s earlier. Human body movement and moisture in fabric layers affect heat transfer process between the human body and thermal environment，thereby their impact on the accuracy of rescue assessments cannot be ignored.