We have studied the magnetic reversal process of magnetron sputtered Pt/Co multilayers by using a magneticforce microscope with in situ bias magnetic fields. In thin films, magnetic reversal is usually dominated either bydomain nucleation or by domain wall motion. In our experiments, a series of magnetic images in situ capturedin the same area indicates that the magnetic reversal in Pt/Co multilayers is dominated by domain nucleation,instead of domain wall motion. In addition, the. local demagnetized curve was obtained by using the bearinganalysis of the domains in the series of magnetic images.