Abstract: The effects of mechanized sowing summer maize（Zea mays L.）by sparse breaks up were explored with different varieties and grades sparse by field testing. The grade of deficiency seedlings and broken ridge and the yield with its component were discussed. The results showed as follows: the main causes of yield reduction by sparse breaks up were the ears decrease. With the adding of grade of sparse breaks up, the yield gradually decreased. The decreased amplitude of yield is less than the increased amplitude of sparse breaks up grade .On the situation of the grade among 10.00%～40.00%, decreased amplitude of yield is 3.60%～28.51%. The decreased amplitude of yield of Ludan 981was bigger than Zhengdan 958 with the same sparse breaks up.