For development of high yield wheat cultivars, this study was conducted to estimate the general combining ability (GCA) of parents, specific combining ability (SCA) of hybrid progenies, heritability and heterosis of grain yield and some agronomic traits. A partial diallel crosses which obtained in a set of six wheat genotypes were sown in randomized complete block design at Gachsarann agricultural research station in 2013-14 growing season under dryland condition. The results of this study revealed a significant difference among the genotypes for all of the traits that indicating considerable genetic variation. Significant effects of GCA and SCA indicated role of additive and non-additive gene action in the control of all considered traits. The mean square ratio of GCA to SCA and Baker genetic ratio showed a preponderance of non-additive gene action for all of the studied traits. Broad-sense heritability was high (0.67-0.99) for all of them, which indicated the role of genetic factors compared with non-genetic factors for controlling of these traits. Narrow-sense heritability was low to moderate (0.06–0.37). Among the parents, Koohdasht was the best general combiners for early growth vigor, days to maturity, spike length, peduncle length, flag leaf extrusion and grain yield. The Koohdasht × DAMARA-6 hybrid showed the best specific cross for days to heading, days to maturity, grain filling period, plant height, chlorophyll content, canopy temperature, grain length and grain yield. These hybrids showed positive and significant heterosis for grain yield, chlorophyll content and grain length and negative heterosis for plant height. It is expected to produce desirable segregants and could be exploited successfully in wheat improvement programs. In addition, because of preponderance of non-additive gene action for studied traits, particularly in the early generations, efficiency of genetic selection was low and selection for genetic improvement of these traits must be retraced in advanced generations.