The current noticeable climate change that has a significant impact on the environment and agricultural systems has become a serious concern for human society. Followed by the industrial activities of the global community and increased concentrations of greenhouse gases in the atmosphere, these changes are still considered as a threat to food safety and the environment. Changes in minimum and maximum temperature, rainfall amounts, and precipitation pattern, changes in CO2 concentrations, and complex interactions between these factors and different crops are studied in the form of different probabilistic scenarios to get a glimpse of the future cultivation situation. Agriculture in Qazvin Plain is based on the water transferred from Taleqan Dam and groundwater. Since today these resources are facing issues like restriction on transfer and draw off, which is because of growth of interest in city dwelling, inappropriate water consumption patterns and over-exploitation, agriculture is sensitive to probable changes in water requirements and it is necessary to predict these changes for better management in the future. This study was carried out to investigate the effect of climate change on growth indices for three crops including wheat, barley, and maize in Qazvin Plain with different possible climate change scenarios, in the form of five large-scale climate models (Hadcm3, CSIRO-MK3, GFDL, CGCM3 and MICROC3.2) and three greenhouse gas emissions scenarios (A1B, A2 and B1) and different possible scenario combinations in the next 30 years, 2021-2050 and 2051-2080 (near and far future). On basis of the study results, it suggests that all 4 target station, in average, will have experienced a change between two ratios of 0.5 and 1.4 of the observed precipitation period by the end of 2050, and the mean temperature will have had a change between -0.1 to 1.6 °C relative to the observed period. By the end of 2080 also, precipitation will have fluctuated between the two proportions of 0.5 and 1.7 times of the observed precipitation period and the mean temperature will touch an increase between 0.6 to 2.6 °C. Results showed that biomass production, grain yield, and water use efficiency in three crops of wheat, barley, and maize have increased up to 20 to 40% in future periods in Qazvin region climate. Growing degree-days (GDD) of these three crops have increased by 20%. Trairation has risen by 10% in wheat and maize; however, it was stable on average in the first period and slightly decreased in the second period in barley. The trairation coefficient has reduced by 5% for wheat and barley and has increased by 15% for maize. Results are valid as long as the initial growing conditions of these three plants are done as before, and the irrigation scheduling is performed according to the present period in spite of climate change. Key words: Climate change, Qazvin Plain, Plant Growth Index, Biomass, Grain Yield, Water Use Efficiency, Growing Degree-days (GDD), Trairation.