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To investigate the effect of applying biochar and straw on the improvement of agricultural soils before and after freezing in seasonal permafrost areas, black soil was selected as the research object, and four different regulation measures (BL: blank control;CLS: application of biochar;JLS: application of straw;CJLS: combined application) were set up based on field experiments to analyze the stability of soil aggregates, pore size distribution characteristics and soil moisture characteristic curves. The results showed that the variation of soil physical properties such as soil water holding capacity and hydraulic conductivity was investigated based on the variation of soil infiltration and saturated hydraulic conductivity (Ksat). The results showed that the application of biochar and straw effectively suppressed the adverse effects of freeze-thaw cycles on soil structure, and effectively maintained the stability of soil aggregates. The application of exogenous biomass materials improved soil pore distribution, increased the proportion of intermediate pore size (0.3~100μm) in the early freezing period, increased the proportion of intermediate pore size 19.05%~35.04%, increased the proportion of soil voids (greater than 100μm) by 4.33%~16.22%, and decreased the proportion of very small pore size (0~0.3μm) by 9.09%~18.18% under the combined effect of exogenous biomass materials and freeze-thaw alternation, and with the CJLS treatment performing the best. In the pre-freezing period, the application of biochar and straw increased the cumulative soil infiltration at 60min under tension -5cm by 73.68%, 60.52% and 151.10%, while in the thawing period, the positive effect exerted by freeze-thaw aging of exogenous biomass materials was diminished, and the cumulative soil infiltration was increased by a maximum of 112.28% only. Meanwhile, the application of biochar and straw increased the saturated soil water content before and after freeze-thaw and enhanced the soil water holding capacity, which contributed to the improvement of soil drought resistance in spring. The plant available water content was increased under the dual effect of exogenous biomass materials and freeze-thaw cycles, while Ksat was increased both before and after freeze-thaw, but the difference between the CLS and JLS treatments and BL were gradually slowed down during the thawing period. The results of the study had important implications for the rational application of biochar and straw resources, revealing the response mechanisms of improved soil physical properties.