Backgrounds <p>Diagnosis of crop nitrogen nutrition is an imperative approach for precise nitrogen application in agriculture and mitigating environmental pollution. However, limited research exists on nitrogen nutrition diagnosis and assessment strategies for maize under different irrigation amount.</p> Methods <p>A two-year field experiment was conducted to investigate the comprehensive response of yield, nitrogen residue in soil, leaf area index, and nitrogen nutrition status to three irrigation levels (60%, 80%, and 100% ETc) and five nitrogen application levels (0, 80, 160, 240, and 320&#xa0;kg&#xa0;ha⁻¹).</p> Result <p>The results showed that the maize yield showed an initial rise, which then reached a stable state with the increase of irrigation and nitrogen application level. The residual soil nitrogen increased with the nitrogen application level, while higher irrigation levels result in the downward movement of soil nitrogen towards deeper soil layers. The critical nitrogen concentration (CNc, %) dilution curve model for maize in relation to irrigation level (W, mm) was developed based on leaf area index (LAI): CNc = aLAI^−b; where a = –2.288 × 10⁻⁵W² + 0.018W + 0.588, and b = –4.025 × 10⁻⁶W² + 0.003W–0.286.</p> Conclusions <p>By conducting an integrated analysis of the nitrogen nutrition index and nitrogen residual effect, it is advisable to reduce nitrogen application level appropriately under lower irrigation levels in the northwest of China; however, it is recommended to maintain control within the range of 160 – 240&#xa0;kg&#xa0;ha⁻¹.</p>