Abstract: Based on WOFOST crop growth model, we simulated the impacts of different drought intensities during jointing to tasseling and tasseling to milkripe stages on spring maize biomass and yield in Inner Mongolia. The results showed that the rates of grain-filling intensity, yield, biomass increment and biomass decreased with the increase of drought degree. After rewatering, the grain-filling intensity and biomass increment were rapidly restored to the level without drought. Grainfilling intensities under light drought, moderate drought and serious drought were reduced by 14.8%-15.4%, 40.9%-42.9% and 52.4%-60.8% respectively. Meanwhile, the yields were reduced by 1.9%-6.1%, 9.5%-15.4% and 18.6%-25.8%, the biomass increments were reduced by 12.6%-12.8%, 31.0%-35.5% and 50.4%-50.8%, and the biomasses were reduced by 2.9%-6.1%, 6.9%-19.4% and 12.0%-32.1% accordingly. The grain-filling period was differently affected by droughts from jointing to tasseling and from tasseling to milkripe stage. The yield loss was higher when the drought occurred from tasseling to milkripe stage because the grain-filling intensity at peak and decline phases was both influenced at this developmental stage. The droughts from jointing to tasseling stage and from tasseling to milkripe stage affected the peak and decline phases of assimilate accumulation, respectively. The duration of the impact by drought from jointing to tasseling stage was longer; therefore, the descent rate of biomass affected by drought was more obvious in this period than that from tasseling to milkripe stage.