In order to explore the influence of sand temperature and blood perfusion rate on the temperature field distribution and bone thermal stress of human knee joint during sand therapy, Based on the theory of biological heat transfer and classical mechanics, The variation of temperature field and thermal stress of knee joint during sand treatment was studied by importing CT image data of knee joint into 3D reverse modeling software Mimics to establish a 3D model, and importing the model into Comsol software to conduct numerical simulation of heat transfer. The results showed that the temperature and stress of the knee bones were mainly concentrated on the patella and the tibia, especially on the long bone of the tibia. According to the curve of bone thermal stress change, the average bone thermal stress reached its peak at 20min of sand treatment, showed a downward trend within 20 to 30 minutes, and gradually decreased after 30 minutes with the increase of time. The best time for sand therapy is about 20 minutes, but not more than 30 minutes at most. The blood perfusion rate plays an important role in regulating the temperature field and stress field of human body during sand treatment.