Abstract: Arid and semi-arid regions experience severe water scarcity and intense surface evaporation, which contribute to widespread desertification and heightened ecosystem vulnerability. In these environments, biological soil crusts (biocrusts) constitute specialized surface assemblages formed through microbial mediation, where cyanobacteria, lichens, and mosses bind mineral particles into a cohesive layer. Functioning as a biologically active interface between the atmosphere and soil, biocrusts significantly influence shallow subsurface heat transfer processes. Nevertheless, the systematic quantification of their effects on soil thermal properties and temperature remains limited. In this study, the bare soil and biocrusted aeolian sandy soil (moss crusts and cyanobacterial crusts) of the Loess Plateau was taken as the object. Combined with controlled laboratory experiments and long-term field monitoring, the soil thermal properties and temperature dynamic differences of two typical biocrusts (cyanobacteria crusts and moss crusts) and bare soil at 0-2 cm depth were systematically studied. A self-developed three-needle heat-pulse probe was employed for accurate determination of soil thermal parameters: heat capacity, thermal conductivity, and thermal diffusivity. The results demonstrated that biocrusts significantly altered the physicochemical properties of surface soil, particularly affecting field capacity and equivalent porosity (P < 0.001). Moss crusts increased field capacity by 120.0% compared to bare soil, while total porosity reached 1.4 times that of bare soil. On this basis, biocrusts further significantly influences the soil thermal properties (P < 0.001). Laboratory measurements quantitatively indicated that the heat capacity of moss crusts was 14.2% and 14.6% lower than that of bare soil and cyano crusts, respectively. Besides, the thermal conductivity of cyano crusts and moss crusts was reduced by 41.0% and 31.1% respectively compared to bare soil, while their thermal diffusivity was also reduced by 39.3% and 19.5%, respectively. At field capacity, cyano crusts reached the highest heat capacity (1.88 MJ/(m³·K)), followed by bare soil (1.77 MJ/(m³·K)), and moss crusts was the lowest (1.63 MJ/(m³·K)). The thermal conductivity of bare soil exceeded that of biocrusts by 63.2% on average, while its thermal diffusivity was 55.0% higher. Field monitoring further confirmed that the heat capacity of cyano crusts (1.30 MJ/(m³·K)) and moss crusts (1.49 MJ/(m³·K)) decreased by 21.2% and 9.7% compared to bare soil (1.65 MJ/(m³·K)). Moreover, the thermal conductivity and thermal diffusivity of cyano crusts were significantly lower than those of bare soil, with reductions of 31.3% and 26.9%, respectively. In contrast, moss crusts displayed higher thermal conductivity (0.78 W/(m·K)) and thermal diffusivity values (4.96 × 10^-7 m²/s), which were 1.2 times higher than those of bare soil. Furthermore, following typical rainfall events (32.1 mm), biocrusts consistently suppressed all thermal properties (P < 0.001). moreover, field temperature monitoring revealed that the average soil temperatures of cyano crusts and moss crusts reached 4.83℃ and 5.11℃, respectively, exceeding the bare soil temperature (4.48℃) by 0.35℃ and 0.63℃. However, this warming effect was strongly suppressed during wet periods with higher rainfall, and the temperature difference between the biocrusts and bare soil decreasing by an average of 79.0% relative to dry periods. In summary, biocrusts modulate near-surface soil thermal properties by altering basic physicochemical properties, such as reducing its bulk density and increasing its total porosity, organic matter content, and field capacity, thereby reshaping the solid-liquid-air phase composition of surface soil. These alterations collectively alter the configuration of soil’s solid-liquid-air phases, systematically modulating its thermal characteristics and promoting heat retention within surface soil. Consequently, biocrusts play the important role in regulating the surface energy balance and influencing the restoration of ecosystems in arid and semi-arid regions. This study provides a scientific basis for understanding surface energy balance mechanisms and for ecological restoration practices in arid and semi-arid areas.