The present study deals with the impact of temperature and CO2 projection obtained for different time periods 2020, 2050 and 2080 using HADCM3 factors on the productivity of rice and wheat crop at four stations viz. Pusa, Purnea, Sabour and Patna of Bihar using InfoCrop model performed. The results showed that the simulated yield of rice and wheat decreased in the range of 1.1-9.2 %, 6.1-13.2 % and 15.9-22.4 % from baseline in 2020, 2050 and 2080 respectively over the stations. Decrease in simulated yield in wheat was observed in the range of 3.5-21.1 %, 14.0-37.9 % for 2050 and 2080 for all the stations.