Having a qualitative model of any system helps to analyze and examine it. Plants have different qualitative models to investigate the effects of different substances, including acids and nano-materials, on them. In this article, the effect of iron nano-chelate on the drought stress of Nigella sativa has been investigated. The experiment was carried out as a split factorial design in the form of a randomized complete block design with three treatments in 3 replications. The main plots include three levels of irrigation (50, 75 and 100), the percentage of available water and sub-factors of humic acid with three zero levels of 250 and 500 mg/liter in two times of stemming and the beginning of flowering in the form of foliar spraying and nano iron chelate solution with three zero levels. 1 and 2 grams per liter were applied at the stem and flowering stage. The results showed that drought stress led to a decrease in the average of the studied traits. Applying the treatment of 50% available water leads to a decrease in plant height (8%), the number of main branches (26%), the number of secondary branches (13%), the number of capsules (50%), the number of seeds in the capsule (34%), capsule weight. (21%), thousand seed weight (5%), dry and wet plant weight (41 and 40%), yield per hectare (24%), oil content (2%) and essential oil (31%). Both levels of humic acid led to the adjustment of the effects of stress in such a way that these two levels increased the yield by 16% and 21% compared to the control treatment. Regarding the iron nanochelate treatment, it was found that the levels of 1 and 2 grams per liter led to a 16% and 27% increase in yield compared to the control. In general, the results of the research showed that the combined application of 500 mg/L of humic acid and 2 g/L of iron nanochelate leads to the improve the vegetative and biochemical factors of black seed plant both in non-stressed and stressed conditions.