Legume winter cover crop hairy vetch(Vicia villosa Roth, HV) can supply mineral nitrogen for silage corn by HV cover killed. The purphose of this study was to understand changes of soil mineral N, yield and N uptake of silage corn by N level (0, 135kgFN/ha) and cover cmp(no cover crop: NCC, hairy vetch cover crop: HVC) at field of Crop Experiment Station in 1996. HV growth decreased soil mineral N concentration before seeding corn, but killed HV cover increased concentration of soil mineral N at surface soil (0~7.5cm) at six-leaf stage of corn. Total dry matter(DM) and N uptake of corn averaged over N level was more decreased in HVC than in NCC at silk stage, but N uptake of corn after silk was more increased in HVC than in NCC by N mineralized fiom HV killed, especially in OkgFNJha. N fertilization increased total DM and and N uptake of corn averaged over cover crop, especially more increased the DM and N uptake before silk stage. Early application of N fertilizer was recommendable in netillage silage corn using hairy vetch cover crop.