Abstract: Grain weight improving mechanism of deep tilling root cutting in high yield winter wheat (Triticum aestivum L.) Lu Bu1, Yu Songlie2, Yu Zhenwen2, Miao Guoyuan3 (1.Institute of Agricultural Resources and Regeinal Planning, Chinese Academy of Agricultural Sciences, Beijing, 100081, 2.Shandong Agricultural University，Tai`an 271018, 3.Shanxi Agricultural University, Taigu 030801) Abstract: For having a better understanding of deep tilling root cutting (DTRC) improving grain weight in winter wheat (Triticum aestivum L.), 2 varieties are employed in a 4 treatments trail in 1997-1999. Several physiologic indexes were tested after anthesis of the wheat. The results indicated that DTRC can improve wheat to have a better “source activity ”with denying peak of Pn in flag leaf, denying leaf aging by more chlorophyll and improving root activity. DTRC can enhance wheat “sink activity” with higher SS activity and higher ATP content in youth spikes. DTRC cause leaf SPS more active, help to “flow” 3-PGA to sucrose more effectively. A mechanic model was established to summary the physiologic mechanism of DTRC improving grain weight in high yield winter wheat.