Abstract: Field trails were carried to study the effects of tobacco straw incorporation and potassium (K) fertilizer on rice yield, K uptake and use efficiency, and its substitute for K fertilizer under different paddy soil K levels in tobacco-rice rotation areas. Results showed that both tobacco straw incorporation (2250 kg·hm^-2) and K fertilizer application (75 kg K₂O ·hm^-2) could increase grain yield and aboveground K uptake of rice. The treatment of tobacco straw incorporation with K fertilizer (St+NPK) got the best effect on rice yield compared with the control (NP). In this treatment (St+NPK), rice yields were increased by 13.3%, 17.1% and 13.5% for low-K soil (available potassium content < 100 mg·kg^-1), middle-K soil (available potassium content 100-150 mg·kg^-1) and high-K soil (available potassium content > 150 mg·kg^-1), respectively, compared with NP. Tobacco straw incorporation (St+NP) could increase K fertilizer recovery efficiency and K fertilizer agronomic efficiency. Under the current practice of applying 75 kg K₂O·hm^-2, St+NPK showed no significant effect on K fertilizer recovery efficiency and K fertilizer agronomic efficiency, demonstrating that the recommended rate of K fertilizer might be more than the actual demand of rice growth. More importantly, data of tobacco straw substitute for K fertilizer showed that tobacco straw incorporation could replace 10%-22% K fertilizer during rice growing season, i.e. K fertilizer could be reduced by 7.2-16.5 kg·hm^-2 for rice under the condition of tobacco straw incorporation. Therefore, it was suggested that straw incorporation could reduce the rate of K fertilizer for high-K soil, but the current K fertilizer inputs (75 kg K₂O·hm^-2) should be supplied to get high rice yield and maintain the soil potassium balance for low-K soil and middle-K soil.