Abstract: A field trail was carried out to study the impact of biochar on soil bulk density, soil moisture content, soil temperature and soil aggregate stability in Lou soil. Five treatments of different biochar amounts were set in this study as follows: 0 (B₀), 20 (B₂₀), 40 (B₄₀), 60 (B₆₀), 80 (B₈₀) t·hm^-2. The results showed that, after applying biochar two years, compared with the control(B₀), the soil bulk density in 0-30 cm soil layer significantly decreased by 7.7%-10.9%, and the soil moisture content significantly increased by 10.0%-13.4%. Applying biochar at 40-60 t·hm^-2 could buffer the change of soil temperature, and increase the soil thermal capacity. The water stable aggregates (WR_0.25) with diameters  greater than 0.25 mm significantly increased by 30.3%, the mean mass diameter (MWD) under dry sieving and wet sieving significantly increased by 15.2% and 31.6%, respectively, and the proportion of aggregate destruction (PAD) and unstable aggregate index (E_LT) significantly decreased by 19.1% and 17.5%, respectively. The results indicated that applying biochar could significantly improve the  water thermal properties of Lou soil and increase soil aggregate stability, and the best applying amount was 40-60 t·hm^-2.