The invention provides a method for constructing a magnetic atom point contact. A structural device with an electro-resistance conversion function is adopted; a conductive material is selected as electrodes; a semiconductor or insulator material capable of forming a magnetic nano conductive channel therein through the action of an electric field is selected as a dielectric layer; a voltage is applied between a bottom electrode and a top electrode to drive ion oxidation reduction, so that a magnetic conductive channel is formed; and a reverse voltage is applied, the magnitude of the voltage ischanged, so that the conductivity G of the conductive channel reaches NG0, wherein N is a positive integer or a semi-positive integer, and G0 is quantized conductivity; and magnetic atom point contactis constructed. Magnetic atomic point contacts of different sizes are constructed by the regulating voltage values; and the sizes of the magnetic atomic point contacts can be regulated, so that the magnetoresistance of the device can be regulated.