Abstract: In order to reveal the mechanism of deep tillage on the temperature and humidity of tobacco planting soil and the root growth and yield of flue-cured tobacco, a single factor experiment was conducted in fields via setting two treatments of 30 cm deep tillage and conventional tillage. The variations in soil temperature and humidity of four different arable layers during the whole growth period were studied, and the variations in the number of first and secondary lateral roots and economic traits of flue-cured tobacco were also analyzed. The results showed that there was no significant difference in the average daily temperature of tobacco planting soils between different arable layers, and the variation trend was generally similar. Compared with conventional tillage, the deep tillage reduced the daily range of soil temperature in different arable layers. Viewing from the whole growth period, the relative humidity of soils increased with the deepening of arable layer, the average daily relative humidity of soils under deep tillage was significantly higher at the depth of 30 cm and 40 cm than that of conventional tillage. On the 80th day after transplanting, the depth of tobacco roots in soils under deep tillage deepened by 8.07 cm comparing with conventional tillage, and the difference was statistically significant (p < 0.01). The numbers of first and secondary lateral roots increased by 40.57% and 36.35% respectively, and the differences were significant(p < 0.05). The indexes of economic traits of flue-cured tobacco differed significantly between different treatments(p < 0.05). The yield and output value of flue-cured tobacco increased by 7.44% and 26.51% under the deep tillage treatment comparing with those under conventional tillage. In conclusion, deep tillage can effectively reduce the daily temperature range of soils in the arable layer and increase soil relative humidity, which is beneficial to the growth and development of root system, and thereby promote the yield of tobacco.