A field experiment was carried out in Hubei on effects of potassium and humic acid and their interaction on dry biomass, chemical composition, flavoring substances and organic potassium salt index in flue-cured tobacco, Jinshennong # 1. The experiment was designed to have only two factors, potassium and humic acid, two levels each. Result show that amendment of humic acid to fields the same in potassium level or application of potassium fertilizer to fields the same in humic acid level increased dry biomass of the plants at the early flu-curing stage and the total flavoring substances in, improved chemical composition of the cured leaves and raised organic potassium salt index of the flue-cured tobacco leaves; and interaction between potassium fertilizer and humic acid had some significantly positive effects on contents of reducing sugar, total nitrogen and potassium, nitrogen/nicotine ratio and organic potassium salt index, and its effects on dry biomass and the other chemical properties of flue-cured tobacco were far from the significant level. The application of a high rate of potassium plus humic acid was more conducive to improving the quality of flue-cured tobacco leaves and increasing potassium content and organic potassium salt index of the leaves than application of a low rate of potassium fertilizer plus a low rate of humic acid.