In order to explore the interaction effect of water and nitrogen, approach optimum management pattern and improve water and nitrogen use efficiencies under the degradable film mulching in arid desert drip irrigated farmland, two years’ experiments were conducted under degradable film mulching drip irrigation fields in Wulanbuhe sand areas, Inner Mongolia. There were three irrigation amount levels, including low (165mm in 2016 and 195mm in 2017), medium (247.5mm in 2016 and 292.5mm in 2017) and high (330mm in 2016 and 390mm in 2017), and three nitrogen levels: low nitrogen (140kg/hm2), medium nitrogen (210kg/hm2) and high nitrogen (280kg/hm2) with three irrigation amount treatments under plastic film mulching as control, and the twelve treatments were randomized complete combination design. The effects of different water and nitrogen supplies on maize yield and water and nitrogen use efficiencies under degradable film mulching in arid sandy area were researched, and the coupling model of water and nitrogen about maize in drip irrigated farmland under degradable film mulching was established and optimized. The results showed that the water use efficiency (WUE) under degradable film mulching was significantly lower compared with that under plastic film mulching. However, there was no significant difference in yield, its components and partial productivity of nitrogen (PFPN) under sufficient water conditions. The irrigation and nitrogen amounts would significantly influence the maize yield and the components, WUE and PFPN under degradable film mulching. There were clearly interaction effect among different water and nitrogen treatments, and the lower irrigation amount would restrict nitrogen utilization. The PFPN and maize yield had an average of 36.87% and 37.18% increase in two years’ experiment when irrigation amount was changed from low to medium, however, it was just about 5.93% and 6.22% increase when the irrigation amount was changed from medium to high;the lower nitrogen application also would restrict soil water utilization, the WUE and maize yield had an average of 7.99% and 18.81% increase in two years’ experiment when nitrogen application was changed from low to medium, however, it was -3.66% for WUE, and just 3.35% for yield when nitrogen application was changed from medium to high;the maximum yield in 2016 and 2017 was 13875.16kg/hm2 and 13805.02kg/hm2, respectively, which were all in high irrigation amount and medium nitrogen application treatment. There were good dualistic and quadric regression relationship among irrigation amount, nitrogen application and yield under the degradable film mulching in arid desert drip irrigated farmland, and the determination coefficient R2 for 2016 and 2017 was 0.978 and 0.988, respectively. The main factor analysis for regression model revealed that the effect of irrigation on yield was greater than that of nitrogen, and the yield was increased first and then decreased with the increase of irrigation and nitrogen. The irrigation and nitrogen application under different target yields was obtained through model optimization. In the experiment, the optimum water and nitrogen ratio was high irrigation amount and medium nitrogen application treatment, and the yield was in target range of 13000~14000kg/hm2 with relatively high WUE and PFPN. Therefore, it can be used as a reasonable technical and theoretical reference for the water and nitrogen management under the degradable film mulching in arid desert drip irrigated farmland.