Two-year (2012—2013 and 2013—2014) field experiments were conducted to determine the appropriate supplemental irrigation amount of winter oilseed rape (Brassica napus L.) at stem elongation stage with the ridge and furrow rain harvesting cultivation. Four treatments, including T1, T2, T3 (with supplemental irrigation amounts of 0, 60, 120mm under ridge and furrow rain harvesting cultivation, respectively) and CK (with supplemental irrigation amount of 120mm under flat planting cultivation) were set up to evaluate the effects of different supplemental irrigation amounts on soil moisture content at 0~30cm and 30~100cm soil depths, aboveground dry matter, taproot growth parameters, lateral root density, yield components and water use efficiency (WUE) of winter oilseed rape. The results showed that soil moisture contents at 0~30cm soil depth of T2 and T3 at different periods were obviously higher than those of T1 and CK. Aboveground dry matter at flowering stage and pod stage, taproot diameter and dry weight, lateral root density at 0~10cm and 10~20cm soil depths at pod stage of T2 and T3 were significantly higher than those of T1 and CK, and no significant differences were found between T2 and T3. Compared with T1 and CK, seed yields of T2 and T3 in two years were increased by 50.99%, 58.15% and 53.89%, 61.19%, respectively, and WUE of T2 and T3 in two years were improved by 37.28%, 25.98% and 92.77%, 76.90%, respectively. T3 achieved the highest yield in both years, the average yield, crop evapotranspiration (ET) and WUE of which were 3235kg/hm2, 368mm, 0.89kg/m3, respectively. While the highest WUE with average value of 0.96kg/m3 was determined in T2, with average yield of 3089kg/hm2 and average ET of 322mm. Therefore, compared with T3, T2 could save irrigation amount by 60mm, increase WUE by 8.97%, and the yield was just reduced by 4.74%. From the perspective of saving water and increasing yield, T2 was recommended as an appropriate irrigation schedule and cultivation pattern for winter oilseed rape at stem elongation stage.