Abstract:The relationship between photosynthetic rate and yield of densely planting corn wasstudied by using 14C tracer technique,The results indicated that the photosynthetic rates of corn were not different between varietal types,The photosynthetic rate was higher at 8:00～16:00 of a day(50～70mgCO2/dm2·h),80%of the photosynthetic assimilate in leaf of earwas transperted to other organs,the amount of distributed in ear was 50%～60%.As dense-ly planting increased the amount of ear per unit area,higher yield ot corn was obtained.