The invention provides iron-based nano-crystalline soft magnetic alloy, and belongs to the technical field of soft magnetic alloy. The iron-based nano-crystalline soft magnetic alloy is characterized in that a chemical formula of the iron-based nano-crystalline soft magnetic alloy is FeSiB<c>Cu<d>T<e>RE<f>, and the T represents at least one of Ti, V, Mn, Cr, Mo, Nb, Zr and W, and the RE represents one or two of La, Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho and Er; the a, the b, the c, the d, the e and the f represent atomic percentages of corresponding components, the b ranges from 12 to 16, the c ranges from 4 to 7, the d ranges from 0.5 to 1, the e ranges from 1 to 4, the f ranges from 0.5 to 2, and the a meets an equation of (100-b-c-d-e-f-g). The iron-based nano-crystalline soft magnetic alloy has the advantages that a saturated magnetostriction coefficient of the iron-based nano-crystalline soft magnetic alloy is close to zero, and the iron-based nano-crystalline soft magnetic alloy is high in magnetic permeability and saturated magnetic induction intensity, and can replace cobalt-based amorphous alloy to be applied to the field of manufacture for magnetic cores of precision electronic components.