Inelastic analysis stability is carried out for tapered beams by ANSYS,considering plasticity developemnt,introducing the universal slenderness of beams in which the taper ratio and moment ratio are considered,a new formula of stability coefficient is proposed.For the out-plane buckling of tapered beam-columns,another new formula is proposed in which axial force and moment and sectional properties are taked from the larger end of tapered members,and the moment term in the formula takes a exponent that varies with slenderness and taper ratio slightly.FEM result obtained by analysis is compared with the results calculated from the proposed formula,and the result is agreeable.