An inertial sensor calibration method has steps of mounting an observer device and an inertial sensor of a vehicle carrying on an inertial move, acquiring actual vehicle motion data from the observer device and inertial signal data of the inertial sensor, calculating an integral corresponding to the vehicular dynamic variation model with respect to the inertial signal data to obtain predicted vehicle sensor data and calculating variations of the actual vehicle motion data, acquiring differences between the two calculated data, applying an energy optimization and a discretization to the differences so as to obtain parametric error variances, and feeding back the parametric error variances to the vehicular dynamic variation model to calibrate the parameters associated with offset and scale factor and acquire a calibrated vehicular dynamic variation model. Under the premise of no GPS, electronic compass or pressure sensor, the present invention can secure positioning continuity and reliability.