In Syria, Barley is grown under rainfed conditions in areas receive less than 300mm (zones: 2, 3 and 4), which is characterized by limited water availability and large year to year variability in both total rainfall and distribution . A biotic stresses such as drought, cold, heat , salinity and biotic stresses in addition to low soil fertility and the traditional methods in agriculture production are the limiting factors for barley productivity in Syria. In these agro-climatic environments, landraces and their wild relatives are considered to be very useful as main sources of genetic materials in breeding programs, also its widely recognized that these materials could be an important source of useful genetic variation. A study of the genetic structure of landraces may explain to what extent their adaptation to harsh environments is associated with remote or continuous introgression of H. spontaneum, and hence indicates an additional avenue to improve barley yield and its stability in dry areas. The ability of pure lines to sustain yield and stability in dry areas highly correlated with its heterogeneity. and the mixture of several lines gave higher productivity than the pure line Arabi asswad. The objectives of this work were to study the relationships between the genotype and environment interaction, to evaluate and compare the performance of number of populations and barleymixtures with pure barley lines under rainfed conditions (Zone2) in Tel Hadya Research Station (35 Km South of Aleppo city). The study also aimed to investigate the population dynamic behavior of three pure lines of barley in pure stands and in mixtures, each pure line being selected from landraces of three climatically/ ecologically different regions in Syria and Jordan. The results showed that, in spit of the narrow genetic variation between the experimental materials, the variations were very wide and obvious for most of the studid characteristics, mainly on grain yield (3.25-5.17 ton/ha) and biological yield 7.4 – 11.9. The variation was due to highly productive tillers, 1000 kernel weight and grain size as well as the morphological and phenological characteristics. The environmental conditions during the three seasons did not allow the evaluation of the reaction of the Mixtures and Populations even though mixture 2, which consists of 1: 2: 1 of zanbaka, Arta and Wadi Al-Hassa showed a very good performance in grain yield, biological yield and many other characteristics such as grain weight, harvest index, threshing percentage, grain number and grain weight. It is expected that pure lines will perform better in favorable and stable conditions and mixtures and some populations will play a very important role under stressed environments.