In semiarid areas, cereal crops often allocate more biomass to root at the expense of aboveground yield. A pot experiment was conducted to investigate carbon consumption of roots and its impact on grain yield of spring wheat(Triticum aestivum L.) as affected by water and phosphorus(P) supply. A factorial design was used with six treatments namely two water regimes(at 80–75% and 50–45% field capacity(FC)) and three P supply rates(P1=0, P2=44 and P3=109 μg P g–1 soil). At shooting and flowering stages, root respiration and carbon consumption increased with the elevate of P supply rates, regardless of water conditions, which achieved the minimum and maximum at P1 under 50–45% FC and P3 under 80–75% FC, respectively. However, total aboveground biomass and grain yield were higher at P2 under 80–75% FC; and decreased with high P application(P3). The results indicated that rational or low P supply(80–75% of field water capacity and 44 mg P kg–1 soil) should be recommended to improve grain yield by decreasing root carbon consumption in semiarid areas. A semi-pot experiment was conducted to investigate carbon consumption of roots and its impact on grain yield of spring wheat (Triticum aestivum L.) as affected by water and A factorial design was used with six treatments in two water regimes (at 80-75% and 50-45% field capacity (FC)) and three P supply rates (P1 = 0, P2 = 44 and P3 = 109 μg P g-1 soil). At shooting and flowering stages, root respiration and carbon consumption increased with the elevate of P supply rates, regardless of water conditions, which achieved the minimum and maximum at P1 under 50-45% FC and P3 under 80-75% FC, respectively. However, total aboveground biomass and grain yield were higher at P2 under 80-75% FC; and decreased with high P application (P3). The results indicated that rational or low P supply (80 -75% of field water capacity and 44 mg P kg-1 soil) should be recommended to improve grain yield by decreasing root carbon consumption in semiarid areas.