The invention discloses an iron base sub-nanometer alloy with excellent manufacturability and a preparation method thereof. A component formula of the alloy is FeaSibBcCudMeXf, wherein M is at least one element of Ti, Zr and Hf; and X is at least one element of C, Ge, V, Cr, Mn, Mo, W, Zn and Sn, and satisfies the following conditions: a is not more than 86 and not less than 75, b is not more than 9 and not less than 2, c is not more than 20 and not less than 10, d is not more than 3 and more than 0, e is not more than 3 and more than 0, f is not more than 2 and not less than 0, e/d is not more than 2 and more than 0.5, and a+b+c+d+e+f=100. The alloy is prepared into a quenching-state strip by a melt quick quenching method, and a lot of alpha-Fe grains and atom clusters with sub-nanometer sizes are dispersed therein; and after the quenching-state strip is heated under proper conditions, a lot of alpha-Fe grains with nanometer sizes can be further separated out, and such excellent soft magnetic properties as high saturated magnetic induction strength, low loss and high magnetic conductivity are achieved. The novel alloy contains no Nb and volatile P elements, and is lower in cost and excellent in production process. A crystallization process of the series of alloy adopts quick heat treatment to prominently improve industrial production efficiency.