The invention discloses a preparation method of an electromagnetic shielding foamed composite material. A nanometer carbon conductive fiber material added to alloy has good electromagnetic shielding ability, and the nanometer carbon conductive fiber material contains treated graphite having good dispersibility and treated nanometer carbon fibers, so the nanometer carbon conductive fiber material has improved electrical conduction property, can be easily compounded with a conductive polymer, and also has strong physical properties, thereby the prepared composite material has good resilience, high tensile strength, good flame retardation property and good electromagnetic shielding property, and can meet the application demands in the fields of electronic packaging and fireproofing.