Abstract Freezing-thawing deformation is a common phenomenon in seasonal frozen soil areas. Based on indoor simulation experiments, the effects of biochar application amounts (0%, 1%, 2%, and 3%) on freezing-thawing deformation characteristics and the response relationships with soil properties were studied. The results showed that (1) the essence of freezing-thawing deformation is the transformation of soil pore sizes from small to large. The biochar application reduced the transformation range and rate, significantly increased the soil total porosity, promoted thaw settlement and restrained frost heaving. In addition, with increasing numbers of freeze–thaw cycles, the soil total porosity increased with low application amounts (0% and 1%) but decreased with high application amounts (2% and 3%). (2) Freeze-thaw cycling reduced the soil aggregate stability, and the application of an appropriate amount of biochar alleviated the decreasing trend, increased the stability of aggregates, reduced the proportion of silt and clay (