In order to study the effect of biochar on hydrodynamic parameters of northeast meadow black soil, five levels of biochar with different volume ratios (0, 2%, 4%, 6% and 8%) were added into soil. The geometric model was set up by using proportion of biochar and soil, and assumed that the soil and biochar all conformed to the VAN GENUCHTEN model, and the equation of soil water characteristic curve was deduced. And by the theory of MUALEM, the relative hydraulic conductivity equation and water diffusivity equation of soil were deduced. Compared experimental results with theoretical analysis results of soil water characteristic curve, it was showed that the porosity increased in soil was not caused by the pores of biochar, it was caused by biochar and surrounding soil aggregate or the gap produced by itself. Biochar was packaged by soil aggregate, made the saturation changed with matrix suction, was close to the saturation of soil without added. When the matrix suction was lower than 2000cm, biochar can greatly improve the water content of soil, but when the matrix suction was higher than 8000cm, biochar can reduce the water content of soil. Because the biochar packaged by surrounding soil aggregate, the theory model was modified according to the experimental results, and the relative hydraulic conductivity equation and water diffusivity equation were deduced. Soil water diffusivity experiment showed that the water diffusivity equation can accurately describe the hydraulic properties of soil that added biochar, and biochar can decrease the soil water diffusion. Finally, the equations of soil water characteristic and relative hydraulic conductivity were used, and the problem of rainfall infiltration was numerically calculated. The relative error of numerically simulated soil water content afetr rainfall with the results of field experiments was less than 13.3%. It was showed that the hydraulic properties of soil that added biochar can fit the equations of the deduced theoretical model. The research results of the soil hydrodynamic parameters of soil can provide the basis of agricultural soil and water conservation and utilization for the northeast black earth area.