Ridge-furrow with plastic film mulching and nitrogen fertilization has been shown to improve soil conditions and plant growth, but it is still unclear how the above-mentioned agronomic practices regulate carbon assimilating (source) and carbon reservoir (sink) to increase winter wheat yield and water use. A field trial was conducted with planting patterns (flat planting with non-mulching (FP) and ridge-furrow with plastic film mulch (RP)) as main plots and N rates (0, 90, 180, and 270 kg N ha–1, marked as N0, N1, N2, and N3, respectively) as sub-plots. The results showed that RP significantly increased soil water storage (SWS), soil temperature (except that at the milk and dough stages of the 2019–2020 season), net content of soil mineral N, and consumption of soil mineral N by 3.8%− 13.5%, 1.4–5 ℃, 7.2%− 197.9%, and 15.1%− 595.7%, respectively, but significantly decreased evapotranspiration during the growth stages (
), total ET (
) of 2019–2020, and WUE by 9.90%, 7.28%, and 11.52%, respectively, compared with FP. Nitrogen application significantly decreased SWS and soil temperature by 9.3%− 22.9% and 5.1%− 21.1%, but increased net content of soil mineral N, consumption of soil mineral N,
,
, and WUE by 45.9%− 512.4%, 15.0%− 22.0%, 6.0%− 50.3%, 8.98%− 25.32%, and 38.50–145.75%, respectively, compared with N0. Soil water storage at the anthesis, milk, and dough stages and soil temperature at the milk stage mainly increased the source and establishment of the initial reservoir, while the soil mineral N mainly optimized the source-sink balance in the middle and late period. However, leaf area and dry matter at anthesis, chlorophyll content at 18 days post-anthesis, and grain number, especially spike number, played decisive roles in increasing yield, while leaf area and dry matter at the milk stage, grain volume at 30 days post-anthesis, and especially the post-anthesis contribution rate for dry matter accumulation in grains, were the main limiting factors. Therefore, ridge-furrow with plastic film mulching combined with 180 kg N ha−1 could balance the source-sink, but it is necessary to study the ratio of ridge-furrow and sowing rate to achieve a high yield and WUE.