Abstract: With wheat straw biochar and dry farmland ash sierozem soil as the research object, by the different proportion of the soil（1%,3% and 5%）,the influence of wheat straw biochar on the physical and chemical characteristics of ash calcium soil and the influence of biochar under different water content are studied.The pH value is measured by potential method, soil organic matter is measured by potassium dichromate capacity method, soil volume density is measured by ring knife method, porosity is measured by the method specified in GB/T 24203-2009,and soil thermal physical properties（volume heat capacity, thermal conductivity, thermal diffusivity） are measured by thermal pulse method.The results showed that when the Biochar is at 1%,3% and 5% respectively, the pH is improved by 0.32,0.43 and 0.14,while the soil organic matter content is increased by 5.64,4.29 and 2.29 g·kg^-1,the soil volume is increased by 0.22,0.19 and 0.17,and the porosity is increased by 11%,26% and 29%.Then, the amount of biochar added was significantly correlated with pH value, organic matter and porosity（P＜0.01） and positively, and negatively correlated with capactive density（P＜0.01）.Under the influence of water content on the thermal physical property parameters of sierozem soil, the volume heat capacity and water content shows a linear positive correlation（R²＞0.952 0,P＜0.05）,while the thermal conductivity and water content shows a logarithmic correlation（R²＞0.995 3,P＜0.05）,and the thermal diffusivity is opposite.The results of this study provide a reference for explaining the effects of biochar on the thermophysical properties of sierozem soil.