Abstract: Aiming at the microclimate changes in tobacco fields, full automatic recorder of microclimate was used in 2000 – 2001 to study the temperature and relative humidity (RH) at the points of 150 cm above ground, soil temperature in depth of 5cm, 10 cm, 15 cm, 25 cm and 35 cm, and RH in soil depth of 20 cm. The results indicated that the minimum and maximum air temperature occurred at 6:00 and 15:00, respectively, which changed little with the increasing growth stages, whereas the extreme value of soil temperature occurred later than that of air temperature in different growth stages. The diurnal variations on air temperature and soil temperature could be simulated by sinusoid: . Because of transpiration of tobacco plants, the air RH ascended in early stage, with peak point in middle stage, and slight descending in later stage. The maximum and minimum air RH appeared at 6:00 - 7:00 and around 14:00, respectively. Soil relative humidity reached its peak (35%) in rapid growth stages, yet descended with the increasing harvest time, while no evident changes were found in the diurnal variations on soil relative humidity.