This research is focused on utilizing cotton simulation model (GOSSYM) to investigate the impact of different dependent variables such as different amount of Carbone Dioxide, rainfall, different Nitrogen Level, UV-B with or without irrigation, or different soil type in a MID-season cultivar for predicting and finding the influence of environmental factors on cotton yield, plant height, main stem nodes, and major phenological events such as squaring, flowering and boll opening during 30 years from 1964 to 1993 in Razan, Hamedan, Iran.