The AMS-02 magnetic spectrometer was installed on the International Space Station (ISS) in May 2011 and has since then been successfully collecting data. One of its main sub-detectors, the silicon tracker, determines the trajectory and absolute charge (Z) of cosmic rays by multiple measurements of energy loss in nine layers of double sided silicon micro-strip detectors. In this contribution we describe the procedure that has been used to accurately calibrate the tracker response and optimize its performances in terms of charge resolution.