The invention relates to a multi-stage medical sewage sterilization device and method based on graphene nano technologies. The multi-stage sterilization device comprises multiple stages of graphene nano composite sterilization grids, a graphene photocatalytic sterilization tank, a graphene-modified diatom ceramic disinfection tank, an ultrasonic sterilization tank and a laser and near-infrared sterilization device. Compared with a traditional method, the present invention has a more thorough killing or blocking effects on pathogenic bacteria, parasite eggs and the like in various medical sewages. In addition, the device of the present invention can be disassembled and cleaned regularly, and has a long service life, thus the process cost is reduced.