Floret size and number are two critical traits for monitoring the floral development and degeneration in wheat, so we measured floret size and number according to the seven stages. Spike dry weight at anthesis (SDWa) is considered as an important factor for the determination of grain number in wheat. Here we found connections between anther and ovary size and SDWa. In addition, we also determined the influence of detillering on the floral abortion process and tried to explain the influence by increased assimilate partitioning to the spike. Moreover, we found an association between ovary size and grain setting, suggesting an important role of ovary size in the determination of grain number per spike/spikelet. After the physiological analysis of floret size and number, we conducted the GWA mapping of traits associated with floret fertility, assimilate partitioning and spike morphology to assess genetic factors for the regulation of floret fertility and its genetic associations between assimilate distribution and spike morphology.