Soil thermal conductivity (λ) is an important thermal property for environmental, agricultural, and engineering heat transfer applications. Existing λ models for frozen soils are complicated to use because they require estimates of both liquid water content and ice content. This study introduces a new approach to estimate λ of partially frozen soils from air‐filled porosity (n a), which can be determined by using an oven‐drying method. A λ and n a relationship was established based on measurements for 28 partially frozen soils. A strong exponential relationship between λ and n a was found (with R2 of 0.82). Independent tests on 10 partially frozen soils showed that the exponential λ‐n a model produced reliable λ estimates with a RMSE of 0.319 W m−1 K−1, which was smaller than those of two widely used λ models for partially frozen soils. The λ‐n a model is easier to use than existing models, because it requires fewer parameters. Note that the λ‐n a model ignores the effect of temperature on λ of frozen soils and is most applicable to soil at temperatures ≤ ‐4°C.