Drought stress, which is the most serious environmental factor reduces crop productions, might be balanced by some free living and symbiotic soil microorganisms. The physiological response of sweet sorghum plants to inoculation with arbuscular mycorrhizal (VAM) fungi and three potassium fertilizer levels (75, 100 and 125% of recommended rate) was evaluated under three different irrigation intervals (8, 12, and 16 days). A factorial experiment was conducted based on a randomized complete block design (RCBD) with three replications in sandy loam calcareous soil at the El-Nubaria region. The results evidenced that water deficit stress inhibited the growth, biomass of vegetative and reproductive parts, and grain and sugar yield. In all inoculated and uninoculated plants, decreased 1000 grains weight, stalk, grain, biomass, dry matter and sugar yields with increasing irrigation intervals. At the same time, inoculation of sweet sorghum with mycorrhiza resulted in a significant increase in the root colonization, number of mycorrhizal spores, alkali phosphatase, the biomass and sugar yield. Also, increase significantly the content of N, P and K nutrients in plant tissue underwater deficit in calcareous soils compared with non-inoculated plants. Potassium fertilizer in combination with mycorrhizal inoculant on all measured traits could make the plants more tolerant to water stress higher than non-mycorrhizal treatments. In general, the results of this study presented that the sweet sorghum plants inoculated with mycorrhiza and 115 kg K2O ha-1 of potassium sulphate fertilizer improved water stress tolerance, increased the sweet sorghum biomass and sugar yield under water deficit stress in comparison to uninoculated plants.