The invention discloses a device for rapidly measuring the grain size and magnetic domain wall width of an oriented silicon steel sheet. The device comprises a sample platform and a developing component, wherein the developing component comprises a display window and a contact layer; the display window is a transparent glass plate or a transparent hard plastic plate; a liquid storage cavity used for containing a developing suspension liquid is formed between the display window and the contact layer; the display window is provided with a suspension liquid injection hole used for injecting the developing suspension liquid into the liquid storage cavity and a liquid storage cavity closed hole used for balancing the internal pressure of the liquid storage cavity; the suspension liquid injection hole and the liquid storage cavity closed hole can be opened or closed as needed; a magnet yoke is arranged in the sample platform and is provided with a magnetizing winding; after being electrified, the magnetizing winding is capable of magnetizing the oriented silicon steel sheet put on the sample platform. By virtue of adopting the powder pattern method theory, the device is capable of rapidly measuring the grain size and magnetic domain wall width of the oriented silicon steel sheet.