The Alpha Magnetic Spectrometer (AMS-02) is an astroparticle physics detector that has been installed on the International Space Station (ISS) in May 2011. The purpose of the experiment is to study with unprecedented precision and statistics cosmic-ray particles in an energy range from 0.5 GeV to few TeV. The AMS-02 Tracker system accurately determines the trajectory and absolute charge (Z) of cosmic rays by multiple measurements of the coordinates in nine layers of double-sided silicon micro-strip detectors. Given the high dynamic range of the front-end electronics, nuclei from hydrogen up to iron and above can be identified. The charge resolution could be naturally degraded by a number of detector effects that need to be carefully accounted for. In this contribution we describe the procedure that has been used to accurately calibrate the Tracker response. Finally we will discuss the Tracker calibration stability with time.