Abstract: Based on the theories of wave propagation in single-phase and unsaturated porous thermoelastic media, a free-field model for unsaturated soils under plane P-wave incidence is established, and the Helmholtz vector decomposition principle is employed to analyze the wave fields in the free field of unsaturated soils under the action of thermal effects, and analytical solutions for the seismic response of the free field of unsaturated soils under the action of thermal effects with plane P-wave incidence are obtained. The influences of thermal physical parameters such as thermal conductivity, medium temperature, and thermal expansion coefficient on the seismic response of a free field of unsaturated soils is analyzed through numerical calculations. The results show that the displacement magnification factors of the ground obtained under the two theoretical models considering and not considering thermal effects have apparent differences. The horizontal displacement magnification factor gradually increases with the increase of the thermal conductivity, but the vertical one is almost unchanged. The horizontal displacement magnification factor gradually increases with the increase of the coefficient of thermal expansion, while the vertical one decreases gradually. With the increase of the medium temperature, the horizontal displacement magnification factor decreases, and the vertical one gradually increases. In addition, with the increase of the saturation degree, the horizontal displacement magnification factor gradually decreases, and the vertical one gradually increases, which indicates that the existence of gas phase in the soils has a significant influence on the surface displacement magnification factor.