To improve water and nitrogen (N) fertilizer use efficiency, increase sustainable agricultural production, and explore the appropriate substitution level of inorganic N fertilizer by organic fertilizer in the semi-arid region of the western Loess Plateau, a three-year field experiment was conducted at the Dingxi Agri-ecological Station in 2016-2018. We examined the effects of commercial organic fertilizer substitution on maize grain yield as well as the use efficiency of water and N fertilizer under plastic film fully mulched ridge-furrow in dryland. There were six fertilizer treatments: T1, N fertilizer without organic fertilizer; T2, substitution 50% inorganic-N with organic-N; T3, substitution 37.5% inorganic-N with organic-N; T4, substitution 25% inorganic-N with organic-N; T5, substitution 12.5% inorganic-N with organic-N; and CK, no N fertilizer. The results showed that treatments of commercial organic fertilizer substitution (T2-T5) had higher grain yield and water and N efficiency than that in T1 treatment in dry year under 200 kg N·hm-2. The changes in grain yield and water and N fertilizer efficiency had no significant difference in treatments of commercial organic fertilizer substitution compared to T1 treatment in wet year. T2 and T3 treatments increased grain yield by 15.6% and 18.2%, and with 35.1% and 27.0% enhancement in harvest index compared to T1. T2 and T3 treatments increased water use efficiency, rainfall use efficiency, N agrono-mic efficiency and partial productivity of N fertilizer by 17.4% and 22.3%, 15.7% and 17.7%, 15.6% and 18.0%, 155.2% and 179.3%. These results demonstrated that under the same N input level, 50% and 37.5% substitution inorganic-N with organic-N could be a suitable substitution rate under plastic film fully mulched ridge-furrow, which could be recommended as a fertilizer application pattern in this area.