Humic acid (HA) and potassium silicate (PS) are bio-stimulants that can improve cowpea growth and yield under water deficit conditions. This study aimed to investigate the mechanism of using 500 mg L^-1 HA and 500 mg L^-1 PS in improving the Vigna unguiculata, cvs. Sudany and Dokii 331 growth and yield under water deficit conditions. The experiment was conducted in a split-split plot with three replications. During two successive growing seasons and irrigation intervals, treatments (5, 10, and 15 days (100, 80, and 50% irrigation requirements) were assigned to the main plots, cowpea genotypes (Sudany and Dokii331) were assigned to the sub-plots, and bio-stimulants (Control (distilled water), HA and PS at 500 mg L^-1) were assigned to the sub- subplot. In this study, the application of 500 mg L^-1 HA and 500 mg L^-1 PS significantly increased plant height, root length, leaf area, number of branches, fresh and dry weights per plant, pod length, number of pods per plant, weight of 100 seeds, and seed yield per plant, especially in the Sudany cultivar. PS also increased electrode leakage (EL) and relative water content (RWC), increasing plant water stress tolerance. HA improved soil properties, including organic matter, total N, available P and K, and dry matter, decreasing calcium carbonate content, salinity, and pH. Overall, the study found that PS and HA can improve cowpea growth and yield under water deficit conditions. Still, PS is more effective for the Sudany cultivar and HA is more effective for soil improvement.