Abstract: Water-tobacco project program was carried out in karst region of Southwest China, at Bijie Prefecture as one of important tobacco production areas of Guizhou province. To evaluate fertilization and watering in water-tobacco project on level terraces of karst region and their effects on quality of tobacco leaves through threshold methods of potassium requested for soil and tobacco, soil pH, soil temperature and water saturation were tested in situ, and potassium elements of soil and tobacco were analyzed. The results showed that the soils on different sections of slope farmlands had differential water storage ability, following the order: lower slope>middle slope>upper slope. There were not evident differences in total potassium contents of soils among three sections of a slope, but great differences in available potassium contents existed, up to 188 mg/kg in topsoil of lower slope. Potassium contents in tobacco leaves varied from 7.4-31.9 g/kg, more than 20 g/kg only in tobacco leaves from lower slope farmlands, following the order: lower slope>middle slope>upper slope. So, differential managements of fertilization and watering are proposed to improve quality of tobacco leaves for water-tobacco project conducted on slope farmlands of karst areas due to their heterogeneity in keeping entropy and fertilizers.