Abstract:A field experiment was conducted to study effects of root pruning at different growth stages on root distribution, root efficiency, yield and water use efficiency (WUE) of winter wheat. The experiment was carried out from October 2005 to June 2006 in the dry tableland on Loess Plateau. Plants were subjected to four treatments: (1) the secondary lateral roots at one side were partially cut off during over-wintering stage (WS), (2) the secondary lateral roots at both sides were partially cut off during over-wintering stage (WB), (3) the secondary lateral roots at one side were partially cut off during jointing stage (GS), (4) the secondary lateral roots at both sides were partially cut off during jointing stage (GB). The intact plants without any cutting were taken as the control (CK). Results showed that all root pruning treatments had significantly less total root biomass than CK in 0-120cm soil layer at flowering stage. Root pruning reduced significantly root biomass of winter wheat in the upper soil layer (0-20cm). Both WS and GS treatments had more root biomass than CK in the middle-layer (40-80cm). All root pruning treatments had significantly higher stomatal conductance (Gs)and transpiration rate (Tr) than CK after anthesis, which suggested that root pruning weaken the effects on gas exchange by drought signal from roots in the top soil through reducing root biomass. At flowering stage, all root pruning treatments had significantly higher photosynthesis and significantly lower root respiration rate compared to CK. Therefore, root pruning improved root efficiency, ensured more photosynthate allocation into grain and increased the harvest index of winter wheat. WUE in WS, WB and GS treatments were significantly higher compared to CK. But WUE in GB treatment was not significantly improved compared to CK. The current study approved the speculation from different wheat cultivars that by optimizing root system distribution soil water consumption in the early growing stage is reduced. Further, negative effects on growth by root drought signal from the top soil after anthesis are weakened, and reduced root respiration favours yield and WUE improvement of winter wheat in arid and semi-arid area.