Information on the nature and amount of genotype × environment (GE) interaction for economic traits and persistence is extremely rare in smooth bromegrass (Bromus inermis Leyss.), especially under drought stress. In this study, 25 half-sib (HS) families of smooth bromegrass were evaluated in the field during five consecutive years under normal and water deficit conditions. The effect of water deficit on dry forage yield was increased from the first year to the fifth, and manifested as a decline in persistence of HS families. Based on narrow-sense heritability estimates, additive gene action was found to be an effective factor in the control of yield components, whereas forage yield is controlled by both additive and non-additive gene actions. Considering the three parameters of stability of combining ability, mean performance and drought tolerance simultaneously, it was inferred that four parental genotypes were superior and stable with high values of general combining ability. This indicates that when developing synthetic varieties from these genotypes, both stability and plant productivity are transmitted to their progenies.