To study the influence of sowing rate, water and fertilizer (N, P and K) coupling on water use efficiency of fodder millet grown in autumn fallow field, taking “Jigu 18” as the tested material, a orthogonal rotation combination with five factors was designed in pot experiment. Results showed that both water and phosphate fertilizer had important impacts on water use efficiency, in which water had the maximum impact, followed by phosphate fertilizer, and nitrogen fertilizer, potassium fertilizer and sowing rate all had no obvious impact. Significant item of sowing rate, water and fertilizer coupling had the below sequence: potassium fertilizer + sowing rate > nitrogen fertilizer + phosphate fertilizer >water+ phosphate fertilizer >water+ sowing rate >water+ potassium fertilizer, and other items had no obvious impact. Mathematical model was established: y=44.26-1.311x1-2.298x2-3.682x3-6.401x4-34.540x5+0.273x1x3+0.118x1x4+0.843x1x5-1.948x2x3+6.631x4x5. The optimal scheme taking economic benefit as the examining index was cleared, that is, soil water content maintained 10%, and sowing rate of fodder millet was 15 kg/hm2. By the scheme, water use efficiency was 26.24 g/kg, and hay yield was 13980.90 kg/hm2, with economic benefit of 13830.90 yuan/hm2, which was 3063.73 yuan/hm2 more than the optimized combination with the highest hay yield, with increase magnitude of 22.15%, and was 6215.15 yuan/hm2 more than the optimized combination with the highest water use efficiency, with increase magnitude of 44.94%. The research could provide theoretic basis and technical support for production practice of fodder millet grown in autumn fallow field.