The invention discloses an Fe-based nanocrystalline soft 
magnetic alloy. The molecular formula of the 
alloy is FeaSibBcMdCuePfAlg, M refers to the metallic element Nb, Mo, V, Mn or Cr, a, b, c, d, e,f and g are mole percentage content of corresponding atoms, b is larger than or equal to 6 but smaller than or equal to 15, c is larger than or equal to 5 but smaller than or equal to 12, d is largerthan or equal to 0.5 but smaller than or equal to 3, e is larger than or equal to 0.5 but smaller than or equal to 1.5, f is larger than or equal to 0.5 but smaller than or equal to 3, g is larger than or equal to 0.5 but smaller than or equal to 10, and the balance is Fe and inevitable trace impure elements; the structure of the Fe-based nanocrystalline soft 
magnetic alloy is the two-phase alloywith the Fe adopting the body-centered cubic structure and Fe(Si, Al) mixed nanocrystalline grains embedded in an 
amorphous matrix, and the 
average size ranges from 10 nm to 13 nm. The invention further provides a preparation method of the Fe-based nanocrystalline soft 
magnetic alloy. The method includes two-step heating and two-step cooling heat treatment. The Fe-based nanocrystalline soft magnetic 
alloy has the advantages of low cost, excellent soft magnetic property, high 
corrosion resistance as well as good manufacturability and heat treatment processability, and has the broad applicationprospects in the fields of 
noise suppression, 
filtration, 
wireless charging and the like in complex and harsh environments.