In semi-arid dryland farming, continuous cultivation of perennial deep-rooted pastures can excessively deplete soil moisture, whereas annual crops underutilize precipitation. We hypothesize that intercropping these two types of plants has great potential for water resource conservation and efficient utilization. A field experiment on wheat-alfalfa strip intercropping was conducted over four seasons from September 2017 to September 2021 to examine root development and water use in three intercrops with wheat-to-alfalfa row ratios of 2:1 (I21), 4:2 (I42), and 8:4 (I84). We observed that wheat roots were primarily distributed within the 0-2 m soil profile, whereas alfalfa roots extended to 5-m-depth. Intercropping reduced vertical penetration while facilitating the lateral extension of wheat roots into alfalfa strips and promoting alfalfa roots distribution laterally below 2-mdepth in the wheat strip. Intercropping also increased root length and surface area of both species. Root plasticity enhanced the complementary use of soil water. Wheat in I21, I42, and I84 absorbed an average of 39.0, 33.1, and 14.7 mm yr-1 of soil water from the alfalfa strip. In the dry year, 2021, alfalfa in I21, I42, and I84 absorbed 19.5, 20.2, and 62.4 mm of soil water from the wheat strip below 2-m-depth. Intercropping increased wheat grain yield by 18.4-22.3 % while maintaining the alfalfa biomass production. The wide-strip pattern, I84, achieved the highest production and water use advantages, averaging 9 % and 13 % respectively, over monocultures, with peaks of 14 % and 31 % in 2021. Our research confirms the feasibility of intercropping shallowand deep-rooted crops to enhance water use efficiency in semi-arid regions, demonstrating a replicable and scalable approach that can be applied globally.