A fracture analysis method for a spot welded portion comprising the steps of: calculating a maximum allowable load value, the maximum allowable load value being a maximum load value at which a crack occurs, of a welded portion in a load fracture mode, a moment fracture mode, and a nugget interior fracture mode based on at least one of a sheet thickness t, a tensile strength TS, an elongation El, and a chemical composition of a nugget portion in each of spot-welded steel sheets, a nugget diameter d of the welded portion, an effective width B of the welded portion determined by a distance between adjacent welded portions, edges or ridge lines, and a sectional height H; and finding the fracture mode where the maximum allowable load value is reached first in the load fracture mode, the moment fracture mode, and the nugget interior fracture mode; calculating an allowable load value at every moment after the maximum allowable load value of the welded portion is reached, in the fracture mode where the maximum allowable load value is reached first in the fracture modes, and finding a displacement or a time at which the allowable load value becomes 0 where a complete fracture occurs; wherein the maximum allowable load value F s of the welded portion in the load fracture mode is calculated as Fs = TS · W · t / α where α is a stress concentration factor obtained by conducting a shear tensile test or a cross tensile test, TS is a tensile strength, W(mm) is a width W (mm) of the test piece and T(mm) is a thickness of the test piece; the maximum allowable load value Mlim of the welded portion in the moment fracture mode is calculated as γ = Mp / M Mlim = Mp ' / γ where M is a bending moment M obtained by conducting a flange tensile test, Mp is a full plastic moment of the test piece and Mp' is a full plastic moment to arbitrary materials, and the maximum allowable load value F s of the welded portion in the nugget interior fracture mode is calculated as Fs = e × Π d / 2 2 × f × C eq + g C eq = Σ i = 1 n t i · C eq i / Σ i = 1 n t i where i is a kind of a test piece, d is a nugget diameter, C eq is a thickness-direction weighted average of a nugget portion carbon equivalent, and e, f and g are coefficients. calculating a maximum allowable load value, the maximum allowable load value being a maximum load value at which a crack occurs, of a welded portion in a load fracture mode, a moment fracture mode, and a nugget interior fracture mode based on at least one of a sheet thickness t, a tensile strength TS, an elongation El, and a chemical composition of a nugget portion in each of spot-welded steel sheets, a nugget diameter d of the welded portion, an effective width B of the welded portion determined by a distance between adjacent welded portions, edges or ridge lines, and a sectional height H; and finding the fracture mode where the maximum allowable load value is reached first in the load fracture mode, the moment fracture mode, and the nugget interior fracture mode; calculating an allowable load value at every moment after the maximum allowable load value of the welded portion is reached, in the fracture mode where the maximum allowable load value is reached first in the fracture modes, and finding a displacement or a time at which the allowable load value becomes 0 where a complete fracture occurs; wherein the maximum allowable load value F s of the welded portion in the load fracture mode is calculated as Fs = TS · W · t / α where α is a stress concentration factor obtained by conducting a shear tensile test or a cross tensile test, TS is a tensile strength, W(mm) is a width W (mm) of the test piece and T(mm) is a thickness of the test piece; the maximum allowable load value Mlim of the welded portion in the moment fracture mode is calculated as γ = Mp / M Mlim = Mp ' / γ where M is a bending moment M obtained by conducting a flange tensile test, Mp is a full plastic moment of the test piece and Mp' is a full plastic moment to arbitrary materials, and the maximum allowable load value F s of the welded portion in the nugget interior fracture mode is calculated as Fs = e × Π d / 2 2 × f × C eq + g C eq = Σ i = 1 n t i · C eq i / Σ i = 1 n t i where i is a kind of a test piece, d is a nugget diameter, C eq is a thickness-direction weighted average of a nugget portion carbon equivalent, and e, f and g are coefficients.