  Quasi-periodic pulsations (QPP) are usually found in the light curves of
solar and stellar flares, they carry the features of time characteristics and
plasma emission of the flaring core, and could be used to diagnose the coronas
of the Sun and remote stars. In this study, we combined the Atmospheric Imaging
Assembly (AIA) onboard the Solar Dynamics Observatory and the Nobeyama
Radioheliograph (NoRH) to observe an M7.7 class flare occurred at active region
11520 on 19 July 2012. A QPP was detected both in the AIA $131\unit{\AA{}}$
bandpass and the NoRH $17\unit{GHz}$ channel, it had a period of about four
minutes. In the spatial distribution of Fourier power, we found that this QPP
originated from a compact source and that it overlapped with the X-ray source
above the loop top. The plasma emission intensities in the AIA
$131\unit{\AA{}}$ bandpass were highly correlated within this region. The
source region is further segmented into stripes that oscillated with
distinctive phases. Evidence in this event suggests that this QPP was likely to
be generated by intermittent energy injection into the reconnection region.
