The wheat lines derived from wide cross between common wheat and Agropyroncristatum contain multi-grain genetic characteristic. The multi-grain wheat line Pubing10969 as well as several major wheat varieties promoted in the Huang-huai winter wheat production region have been selected as plant materials in this study to better understand the developmental process during which this multi-grain characteristic has formed. In this study, the dynamic developmental processes of floret differentiation, degeneration and seed formation between distinct wheat varieties were compared and analyzed by anatomy and statistical methods, to provide theoretical principles for the application of multi-grain genotypes in plant breeding and to uncover the mechanisms underlying multi-grain characteristic. The analysis of variance (ANOVA) results of agronomic traits showed that the multi-grain characteristic of Pubing 10696 was mainly caused by the improved grain/spikelet number per spike, and it did not negatively affect the 1000-grain-weight. The anatomy results of developmental characteristics of plant immature spikes at different stages demonstrated that during panicle differentiation, the initiation and duration time of Pubing10696 were much earlier and longer, respectively, than the check varieties. Besides, the differentiation and degeneration speeds of floret developmental process of Pubing10696 were more rapid and slower than the others, leading to the significantly increased number of florets developed into the tetrad stage. These characteristics were the main causal factors of increased number of florets and more grains developed. To sum up, the developmental characteristics of the immature spikes and florets of Pubing10696 were the determining factors for its multi-floret and multi-grain agronomic traits.