The invention discloses a method for reducing the thermometric error of magnetic resonance and the method is used for an HIFU device for monitoring magnetic resonance imaging. The method comprises the following steps: obtaining an MR phase diagram as a reference image before heating a heating area by the HIFU device; during or after heating by the HIFU device, obtaining another MR phase diagram as a heating image; and calculating the temperature change of the heating area according to the heating image and the reference image. The method also comprises the step of compensating for temperaturechanges according to the magnetic field change caused by the position change of the ultrasonic transducer of the HIFU device. By using the method of the invention, the temperature error caused by theposition change of the ultrasonic transducer can be significantly reduced.