With the same N and P fertilizer rates, the effects of K fertilizer on roots, leaf yield and quality of flue-cured tobacco were studied and their mutual relation was investigated. The results indicated that when the proportion of N and K was 1:2, the total dry matter accumulation, yields, output value, and quality were the highest. There was significantly (1% or 5%) positive correlation between economic character and 40 d and 80 d root dry weight. The 40 d root dry weight was positive correlated with total N, K, and protein contents of tobacco leaves, negatively correlated with total sugar content of X2F, and positively correlated with nicotine of C2F. The 80 d root dry weight had significantly negative correlation with total sugar content of X2F, significantly positive correlation with total N content and K content of X2F and B2F. There was significantly positive correlation between K fertilizer rate and aroma quality, aroma quantity, offensive odor, lingering odor scores and total sensory quality scores.