1. A method for regulating magnetic multi-domain state, comprising: providing a ferromagnetic thin film; applying a current and an external magnetic field simultaneously to manipulate the magnetization state of the ferromagnetic thin film to a stable multi-domain state with a desired ratio between two types of magnetic domains with opposite magnetization directions; wherein the current is configured to drive movements of magnetic domains in the magnetic thin film, and the external magnetic field is configured to regulate generation/annihilation of magnetic domains in the magnetic thin film and state of the magnetic domain during the movement, so that the magnetic thin film is manipulated to a stable magnetic multi-domain state.