A magnetic verification system for bill acceptor including a magnetic induction circuit, a signal amplifying and regulating circuit, and a magnetic field generating circuit, the signal amplifying and regulating circuit having a D/A converter, the magnetic induction circuit having a magnetic device adapted for scanning the magnetic ink of the bill to be verified, the magnetic device being adapted to write a magnetic field reference value from the magnetic field generating circuit into the D/A converter, for enabling the D/A converter to adjust the intensity of light being emitted by a LED of the signal amplifying and regulating circuit onto a photoresistance of the signal amplifying and regulating circuit so as to cause the photoresistance to change the resistance thereof subject to the intensity of light from the LED, so that an operation amplifier at the output end of the magnetic induction circuit obtains the correct magnetic field signal value to verify the authenticity of the inserted bill.