The invention discloses a preparing method and application of a functional AOPAN-AA nanofiber membrane. The preparing method includes the following steps that A, electrostatic spinning PAN nanofiber is processed in an amidoxime mode to prepare AOPAN nanofiber containing an amidoxime active group; B, the functional AOPAN-AA nanofiber membrane is prepared from the AOPAN nanofiber prepared in the step A through atom transfer radical polymerization grafted acrylate. The obtained AOPAN-AA nanofiber membrane is stable in form, high in porosity and large in specific area, and a great number of carboxylic groups are grafted to the surface so that the material can be applied to the fields of macromolecule filtration, enzyme immobilization and metal ion adsorption and has remarkable functionality.