  We perform Differential Emission Measure (DEM) analysis of an M7.7 flare that
occurred on 2012 July 19 and was well observed by the Atmospheric Imaging
Assembly (AIA) aboard the Solar Dynamic Observatory. Using the observational
data with unprecedented high temporal and spatial resolution from six AIA
coronal passbands, we calculate the DEM of the flare and derive the time series
of maps of DEM-weighted temperature and emission measure (EM). It is found
that, during the flare, the highest EM region is located in the flare loop top
with a value varying between 8.4 10^28 cm^-5 and 2.5 10^30 cm^-5. The
temperature there rises from 8 MK at about 04:40 UT (the initial rise phase) to
a maximum value of 13 MK at about 05:20 UT (the hard X-ray peak). Moreover, we
find a hot region that is above the flare loop top with a temperature even up
to 16 MK. We also analyze the DEM properties of the reconnection site. The
temperature and density there are not as high as that in the loop top and the
flux rope, indicating that the main heating may not take place inside the
reconnection site. In the end, we examine the dynamic behavior of the flare
loops. Along the flare loop, both the temperature and the EM are the highest in
the loop top and gradually decrease towards the footpoints. In the northern
footpoint, an upward force appears with a biggest value in the impulsive phase,
which we conjecture originates from chromospheric evaporation.
