In this paper, a novel Bian stone thermal therapy assisted by using solar radiation is proposed for safe thermal therapy on patients. A mathematical model is developed based on heat balance, and the performance of heat transfer from the novel Bian stone thermal therapy system to human body is studied. Sensitivity analysis is also performed. Fluid heated by solar radiation is channeled through a pipe to heat the Bian stone. For stronger solar radiation, or smaller or shorter pipe, the Bian stone attains the initial body temperature faster, and the novel thermal therapy system shows better performance and can therefore be used on patients earlier during the day. Early use of the thermal therapy system is a very important factor because the lowest ambient temperature is normally obtained early in the morning. Moderate water flow velocity is suitable by considering good mixing effect and power savings. The stone-body contact surface area has little influence on the critical heating time for the Bian stone to reach the initial body temperature after sunrise. This work lays a solid foundation for safe use of the solar assisted Bian stone thermal therapy. (C) 2016 Elsevier Ltd. All rights reserved.