Abstract: Fillet weld joints that widely used in engineering is the weakness of structure because of the nonuniform stress distribution. Reduced stress of weld seam was recommended by the International Institute Welding about static load strength of welding seam, which reflected the relationship between with inner shear stress and normal stress to reduced stress. In this paper fracture of fillet weld occurring to section of the maximum reduced stress, using front fillet welded t-shape weld joint as object of analysis, analyzing to relationship of the front fillet weld maximum reduced stress with bearing capacity and dimension of welding seam.Designing sizes based on bearing capacity and equal strength criteria.Numerical simulates to t-shape weld joint by finite element software, its numerical simulation basically agreed with theoretical results. Weld size design of front fillet welded T-shape weld joint based on reduced stress is practicable.