A preparation method for an iron-based super conductor belongs to the technical field of iron-based super conducting materials. A1-xBxFe2As2 (A=Ba, Sr, Ca, Eu, and B=K, Na) and AFe2-xBxAs2 (A=Ba, Sr, Ca, Eu, and B=Co, Ni, Pd, Pt, Ir, Rh, Ru) are prepared, wherein 0<x<=0.7. For the A1-xBxFe2As2, FeAs is prepared first, then AFe2As2 and BFe2As2 are prepared respectively, and the FeAs, the AFe2As2 and the BFe2As2 are mixed and sintered to obtain the A1-xBxFe2As2. For AFe2-xBxAs2, FeAs and BAs are prepared first, then AFe2As2 and AB2As2 are prepared respectively, and the FeAs, the BAs, the AFe2As2 and the AB2As2 are mixed and sintered to obtain the AFe2-xBxAs2. A reacting process can be controlled by means of step reaction, generation of an impure phase is reduced, electromagnetic performanceof the iron-based super conductor is improved, and practicality is improved.