  The decay of sunspot plays a key role in magnetic flux transportation in
solar active regions (ARs). To better understand the physical mechanism of the
entire decay process of a sunspot, an {\alpha}-configuration sunspot in AR NOAA
12411 was studied. Based on the continuum intensity images and vector magnetic
field data with stray light correction from Solar Dynamics
Observatory/Helioseismic and Magnetic Imager, the area, vector magnetic field
and magnetic flux in the umbra and penumbra are calculated with time,
respectively. Our main results are as follows: (1) The decay curves of the
sunspot area in its umbra, penumbra, and whole sunspot take the appearance of
Gaussian profiles. The area decay rates of the umbra, penumbra and whole
sunspot are -1.56 MSH/day, -12.61 MSH/day and -14.04 MSH/day, respectively; (2)
With the decay of the sunspot, the total magnetic field strength and the
vertical component of the penumbra increase, and the magnetic field of the
penumbra becomes more vertical. Meanwhile, the total magnetic field strength
and vertical magnetic field strength for the umbra decrease, and the
inclination angle changes slightly with an average value of about 20{\deg}; (3)
The magnetic flux decay curves of the sunspot in its umbra, penumbra, and whole
sunspot exhibit quadratic patterns, their magnetic flux decay rates of the
umbra, penumbra and whole sunspot are -9.84 * 10^19 Mx/day, -1.59 * 10^20
Mx/day and -2.60 * 10^20 Mx/day , respectively. The observation suggests that
the penumbra may be transformed into the umbra, resulting in the increase of
the average vertical magnetic field strength and the reduction of the
inclination angle in the penumbra during the decay of the sunspot.
