Abstract:Wheat cultivars of different grain weight (representing small or large grain cultivars re-spectively) were selected as experimental materials, the effect of removal of top two spikelets on average grain filling rate, average increment rate of ear weight, photosynthetic rate and partitioning of 14C assimilate during grain filling in winter wheat plant were investigated. When the top two spikelets were removed at anthesis, the average grain filling rate and average increment rate of grain weight per ear increased accordingly, resulting in compensatory increase of grain weight per ear. Compared with large grain cultivars, the increase magnitude of small grain cultivars were much higher. Resulting from strenthened sink activity, the photosynthetic rate of small grain cultivars at middle and final stage of grain filling and the partitioning of 14C assimilate into the grain of all cultivars were increased. Conclusively, both the photosynthetic rate and the partitioning of 14C assimilate were controlled by sink activity, but the regulation mode and magnitude were dependent on the types of cultivar.