Abstract: In order to improve the soil properties of tobacco fields in purple soil regions and mitigate the effect of seasonal drought on the growth of tobacco, the effects of different application rates of a water-retaining agent (0, 30, 60, 90 kg/ha) on soil physical properties, fertility, chemical composition, agronomic and economic properties of flue-cured tobacco Yunyan 87 were studied in the purple soil area of Hengnan County of Hunan Province. The results showed that the water-retaining agent effectively reduced water loss of tobacco-planting purple soil and the reduction effect increased with the increase of the amount of water-retaining agent. The application of water-retaining agent significantly (p<0.05) reduced soil bulk density by 8.44%-11.62% and increased soil non-capillary porosity by 28.65%-33.82%. The increased soil permeability was helpful in promoting the growth and development of tobacco plants. The water-retaining agent improved the overall quality and economic value of flue-cured tobacco. The sugar-nicotine ratio was significantly increased by 1.03-3.50 when treated with water-retaining agent and the content of nicotine significantly decreased by 0.14-0.42 percentage points. During the growth period of tobacco, compared with the control, the yield of flue-cured tobacco and the proportion of superior tobacco increased by 21.90% and 4.66% respectively when the application rate of water-retaining agent was 60 kg/ha. In conclusion, 60 kg/ha is the most suitable amount of water retaining agent for purple soil planting tobacco in our study area.