The current research aimed to investigate the effect of water deficit irrigation and plant density on yield and yield components of promising lines of grain sorghum. The experiment was conducted in a split-plot factorial design with three replications at Seed and Plant Improvement Institute (SPII) for two years (2015-2016). Irrigation was considered as the main factor (60, 120 and 180 mm evaporation from pan class A) and plant spacing on row (8, 12 and 15 cm) and lines (KGS23, KGS32 and KGS36) were as factorial in the subplot. The combined analysis of variance indicated that there was a significant difference between the lines in terms of grain yield (P≤0.01). The lines KGS23 and KGS36 exhibited the highest grain yield at 5333 and 4645 kg ha^-1, respectively, while line KGS32 produced the lowest grain yield of 4011 kg ha^-1. There was a response of grain sorghum lines to irrigation. Under water deficit irrigation, the line KGS23 had a significant advantage in comparison to the other two lines in terms of high yield, morphological characteristics, and adaptation to drought stress conditions. Grain yield was positively correlated with panicle weight, biological yield, and 1000-grain weight. As well, Line KGS36 performed better than KGS32 in terms of grain yield and drought tolerance. The highest grain yield (7964 kg ha^-1) was observed for line KGS23 under normal irrigation and plant space on row spacing of 12 cm in the second year. Moreover, the effect of plant density on grain yield was not significant (P≤0.05).