The invention belongs to the technical field of drinking water purification, and in particular relates to a granular activated carbon loaded nano iron composite filter element material and a preparation method thereof. According to the technical scheme, the preparation method comprises the following steps: (1) pretreating granular activated carbon so as to remove floating ash, improving porosity and increasing surface functional groups; (2) by taking the pretreated granular activated carbon as an adsorption material, loading divalent or trivalent iron ions inside the granular activated carbon by using an ultrasonic oscillation auxiliary solution adsorption method; (3) reducing the iron ions inside the granular activated carbon into nano iron by using a hydrogen thermal reduction method, and controlling the flow of hydrogen, the temperature of thermal reduction and the reaction time, thereby obtaining the zero-valent iron loaded granular activated carbon composite filter element material of which the particle size is smaller than 100nm and the dispersity is high.