Clay sculptures, an important component of China's immovable cultural relics, are usually preserved in grotto temples and temple buildings they embedded in. The physical environment of these buildings therefore affects the distribution of heat and moisture within the clay sculptures, especially on the surfaces. This also results in deterioration such as peeling, cracking, etc. To simulate and assess the stress deterioration generated inside the clay sculptures under the fluctuation of thermal and humidity environment, this paper takes the Arhat statue of Baosheng Temple in Suzhou, China, as an example, and simulated its internal thermal and humidity distribution through the heat and moisture transfer model. Combined with the elasticity mechanics model, this paper selected the points 0.5 cm from the statue surface to calculate the thermal and humidity stress at these points. The simulation and monitoring results show that the simulated maximum thermal and humidity stress at 0.5 cm from the surface of the statue in the in-situ environment is 392 kPa (tensile stress), which means the existence of material damage risk. The simulation shows that the fluctuation of ambient temperature in Baosheng Temple Museum of Antiquities will cause a risk of stress deterioration on the surface of the statue. Therefore, for the preservation of clay statues, the thermal and humidity fluctuations of the physical environment should be reduced.