The invention belongs to the technical field of immune analysis and biosensing detection, and particularly relates to a preparation method and an application of an electrochemical immunosensor based on Hemin-rGO (reduced graphene oxide). A Hemin-rGO (reduced graphene oxide) porous composite material separated by microporous carbon spheres loaded with silver nanoparticles is used as a detection antibody marker, and the constructed sandwich electrochemical immunosensor realizes detection of tumor marker carcinoembryonic antigens, has the advantages of high sensitivity, high specificity, low cost, low detection limit and the like, and has important scientific significance and application value for early diagnosis and disease monitoring of lung cancer.