Abstract: A new calibration method that can increase the estimation accuracy of strapdown inertial measurement unit(IMU)s model parameters is described when the IMUs axes were not oriented precisely with respect to the axes of a tri-axial turntable. An accurate mathematical model was derived firstly. Then a test scheme, which was a combination of the coarse and precise calibration attempts to find the optimized values of the models parameters, was introduced to minimize the error by starting at an initial parameter estimation of the coarse calibration. Test results showed that this calibration method can estimate the installation error and parameters of IMU model precisely without orientation adjustment. The best calibration method is found to be the"30-position" calibration arrangement.