The microstructure and the corrosion property of AZ61 magnesium alloy stirred by permanent magnet (PM) were investigated. Based on the principle of electromagnetic field and magnetohydrodynamics, the force field of liquid metal in a PM field was analyzed. As a result, liquid metal in a PM experiences radial and tangential forces that are cyclically variational both in direction and magnitude. This phenomenon, namely electromagnetic vibration, influences matrix microstructure, subsequently affects corrosion property of the matrix.