Robust ferroelectric films, which are universally associated with defects, require a standard rectangular polarization hysteresis loop to be viable in technological applications. We demonstrate that the polarization of the PbTiO3-Bi(Mg1/2Ti1/2)O-3 based ferroelectric thin films is unusually waked up, and a standard hysteresis loop is obtained. It is first time to directly observe the reorientation of domain fractions by high-resolution synchrotron x-ray diffraction which is the origin of the polarization wake-up, simultaneously corresponding to the piezoresponse force microscopy measurements. The polarization rejuvenation can also be systematically controlled by the poling cycles and defect concentration, which is related to defect rearrangement. The present work provides a picture to understand the physics of defect activity and domain evolution in ferroelectric thin films, facilitating the optimization of the ferroelectric for applications which require a stable polarization.