The spatiotemporal distribution of roots affects a plant's ability to uptake soil resources, which ultimately influences grain yield. A rhizobox experiment was conducted with or without water stress using four winter wheat (Triticum aestivum L.) cultivars with differing drought tolerance (drought tolerant: Changwu 134 and Changhan 58; drought sensitive Xiaoyan 22 and Xinong 979). Plants were grown in soil-filled rhizoboxes under moderate drought (MD, 55% of field capacity) and well-watered (WW, 85% of field capacity) conditions. When exposed to drought stress, the yield of the drought tolerant cultivars were greater than that of the drought sensitive cultivars. Changhan 58 had the highest grain yield and Xinong 979 had the lowest. When well-watered, the highest grain yield was from Xinong 979, while the lowest was from Changwu 134, and the yields from Changhan 58 and Xiaoyan 22 were similar. A correlation analysis showed that root traits at different growth stages was significantly correlated with grain yield. A multiple stepwise regression analysis showed that the subsoil root biomass at stem elongation had a significant positive effect on grain yield, while total RLD (root length density) had a negative effect on grain yield regardless of water supply. A path analysis showed that the order of direct contribution to grain yield was that of total RLD at anthesis (｜0.54｜) > subsoil root biomass at stem elongation (｜0.36｜) > total RLD at maturity (｜－0.31｜) when under moderate drought. When under well-watered condition, the higher direct contribution to grain yield was that of total RLD at maturity (｜-1.56｜) and then subsoil root biomass at stem elongation (｜0.83｜). We conclude that reducing total RLD at maturity and increasing subsoil root biomass at stem elongation contributed to the high yield. The cultivars with increased total RLD at anthesis may increase grain yield in rain-fed dryland agricultural regions.