During the hard magnetism calibration process of compass by traditional methods, the compass was always disturbed and the calibration parameters were relative values. Considering these problems, the errors of anisotropic magneto resistance (AMR) compass were analyzed, the error model of compass was established and a method called scalar calibration was used to calibrate the compass. Compared with the traditional calibration methods of compass, the scalar calibration method didn-t need the reference of head direction. During the calibration of the compass by this method, a great volume test data of any different positions was used to estimate the optimal parameters by iteration. So this method could reduce magnetism disturbance influences through exerting the restraint and the calibration value is the absolute vectors. By the hard magnetism calibration, the precision of compass was improved by 7 times. The experimental result proves the validity and usability of this method.