[Objective]In this study,the formation mechanism of grain quality of soft wheat was investigated to provide support for soft wheat breeding.[Method]Using soft and hard wheat varieties as experimental materials,changes of Rubisco(ribulose-1,5-bisphosphate carboxylase/oxygenase)degradation in flag leaves with different quality types during grain filling stage were investigated.[Result]Chlorophyll content and Rubisco content were both gradually reduced in flag leaves of wheat cultivars with different quality types during grain filling stage.Changes of Rubisco content were insignificant at early grain filling stage,but Rubisco content in flag leaves of soft wheat was higher than that of hard wheat at mid-late grain filling stage.Degradation products of Rubisco large subunits with molecular weight of 51 kD could be detected in flag leaves of various wheat cultivars.Rubisco in flag leaves of hard wheat Zheng 9023 was significantly earlier degraded compared with Yangmai 15,indicating that leaf senescence in hard wheat was earlier than soft wheat,which suggested that the protein accumulation in wheat grains may be related with Rubisco degradation in flag leaves after anthesis.[Conclusion]This study implied the foundation of soft wheat breeding and optimization of cultivation and wheat management in the field. [Method] Using soft and hard wheat varieties as experimental materials, changes of Rubisco (ribulose-1,5-bisphosphate [Result] Chlorophyll content and Rubisco content were both gradually reduced in flag leaves of wheat cultivars with different quality types during grain filling stage. Change of rubisco content were insignificant at early grain filling stage, but Rubisco content in flag leaves of soft wheat was higher than that of hard wheat at mid-late grain filling stage. Degradation products of Rubisco large subunits with molecular weight of 51 kD could be detected in flag leaves of various wheat cultivars. Rubisco in flag leaves of hard wheat Zheng 9023 was significantly reduced degraded compared with Yangmai 15, indicating that lea f senescence in hard wheat was earlier than soft wheat, which suggested that the protein accumulation in wheat grains may be related with Rubisco degradation in flag leaves after anthesis. [Conclusion] This study implied the foundation of soft wheat breeding and optimization of cultivation and wheat management in the field.