Abstract: The effect of loss rate of the corn yield and disease situation by differential ear of head smut plant is investigated in five corn varieties, in order to confirm the yield losses of maize head smut on corn. The results of two sites showed that, part of diseased plants have differential ear that account for 0.51%-14.64% percent of the disease plants in the top leaves. There were four forms of differential ear, normal pollination and seed, normal pollination but undergrain-filling, normal pollination but cannot grain-filling, fail to pollinate. So the loss of yield could be reduced 0.13%-1.27% percent due to the yield of differential ear, so the loss rate of the corn yield was lower than head smut’s incidence.