Rangelands have been composed of different plant species that emergence of phenological stages in every one of them will be influenced by environmental and genetic factors. In order to exploit the time and achieve acceptable performance in each plant species, it is necessary that the emergence of biological phenomena are recorded and studied. The objective of the present study is to survey the different phenological stages of Bromus tomentellus in order to achieve proper management programs in the study area and similar areas. For this purpose, this study was conducted in semi- steppe rangelands of Kordan located in Alborz province for a 4-year period (2007- 2010). Among the plant species under consideration, ten plant bases were selected and recorded in special forms, during 4 years in the growing season, in 15-day intervals at the vegetative stage and in weekly intervals at reproductive stage, occurrence date of plant critical stages including the stages of the growth and vegetative growth, flowering, seed maturation and drying of the plant, along with the information related to the total height of plant in centimeter. In addition, the meteorological data and information relevant to a four- year study include; average monthly temperature and monthly rainfall from the meteorological station closest to the study area were prepared, and by noting the dry period, the Ombrothermic curves for the years 2007-2010 were separately drawn to adapt to the phenological stages of the study plant. The results indicated that this plant species begins its growth by noting the weather conditions, especially environment temperature (degree-day), in different years of the study period. Different phenological stages also have almost constant temperature demand (GDD), which the emergence of the stages is observed after obtaining the required temperature