In order to investigate the effect of humic acid on the quantitative and qualitative yield of flixweed under different drought stress conditions in the form of split plots based on randomized complete blocks with four replications in the research farm of the Faculty of Agriculture, Ghods Branch. The main factor of irrigation in 3 levels includes: normal irrigation, mild stress and severe stress in the main plots and the secondary factor of humic acid in 3 levels including: non-consumption, 100 mg/L, 200 mg/L spraying with humic acid was present in the subplots. The results of analysis of variance showed that the effect of irrigation levels at 5% and humic acid at 1% and the interaction between irrigation and humic acid at 5% were significant. The highest grain yield was related to the treatment of 200 mg/L humic acid under normal irrigation conditions. The results showed that in all irrigation levels, increasing humic acid consumption led to increased grain yield, so that in normal irrigation and mild stress conditions the least difference between humic acid levels and in severe stress conditions the highest difference between humic acid levels was observed. This means that humic acid showed the greatest effect in reducing the effects of drought stress compared to other levels of irrigation (mild stress and normal irrigation).