Abstract: There are two flower types including thrum and pin in buckwheat ,it’s ratio will be approximately 1 to 1 theoretically.the earlier stage research showed that the different varieties of buckwheat existed different ratios among the thrum and pin and different ratio would affect the yield of buckwheat dramatically.this trial used three different varieties introduced from inner Mongolia ,guizhou province and our institute as basic research materials . By setting up the different flower type ratio in which T:P is 1:9 ,2:8 ,3:7,4:6,5:5, 6:4,7:3,8:2,9:1 separately. This experiment was evaluated the seed set by the grain per plant and the weight per plant and discussed the relationship between flower types and seed setting. The result shows that three varieties express high seed setting when the flower type ratio is 4:6 or 6:4, the pin plant have better seed setting than thrum plant when the flower type ratio is near to 1:1. The seed setting would express much more better when this flower type is less in this treatment. it inferred that the buckwheat yield will be reduced when the thrum plant occupied over 80% in the group.