Abstract: The spike differentiation and flowering characteristics in Kentucky bluegrass (Poa pratensis) were closely observed periodically throughout the development stages. The whole spike differentiation could be divided into 5 stages, which were the differentiation stage of first bract primordium, the differentiation stage of primary branch primordium, the differentiation stage of secondary and third branches primordial, the differentiation stage of spikelet and floret primordial, the stage of stamen and pistil primordial formation. The whole flowering progress in a spike of Kentucky bluegrass lasted about one week. The flowering order of the branches in the spike cob was from up to down, but the flowering order of florets in a single spikelet was from down to up, the flowering order of each branch was that the top flower blossomed first and then in bottomup order till the flower in the top of penultimate spike came into blossom. According to the relationships between spike differentiation stages and phenophase, the regulation practices for spike differentiation and yield formation in Kentucky bluegrass should focus on the specific phenophases.