The invention discloses a magnetic fixing device for a building template. The device comprises a magnetic control box, wherein a rotor made of a cylindrical magnetic steel is horizontally disposed inside the magnetic control box, and is rotatably installed inside the magnetic control box along the shaft, one end of the rotor is driven by a handle, a rectangular parallelepiped magnetic steel is fixedly disposed directly above the rotor, and one side of the magnetic control box is provided with a clamping slot, which clamps a steel template. The magnetic fixing device has the advantages that therelative motion of the magnetic system is driven by the rotation of the cylindrical magnetic steel, and the magnetic field intensity on a working magnetic pole surface can be added or subtracted, sothat the purpose of holding and unloading is achieved, the impact force in vertical motion caused by frequent combination of magnetic blocks is avoided, and the problem of scrapping the device causedby the breakage of the neodymium iron boron magnetic steel is solved.