The invention discloses a preparation method of a Cefamandole Nafate powder injection for injection. The method includes the steps of: (1) strain preparation; (2) preparation and culture of seed tank; (3) preparation and culture of a fermentation tank; (4) filtration; (5) decolorization and concentration; (6) preparation of a reaction tank and pipeline; (7) preparation of enzyme catalytic reaction; (8) enzyme catalytic reaction; (9) crystallization; (10) centrifugation and vacuum drying; (11) preparation of 7-ATCA; (12) preparation of cefamandole acid; (13) preparation of Cefamandole Nafate; and (14) aseptic subpackaging, thus obtaining the Cefamandole Nafate powder injection for injection. The invention provides the method of improving the 7-ACA preparation process so as to improve the product quality of cefamandole.