  Using observations from the SOHO, STEREO and Hinode, we investigate magnetic
field evolution in an equatorial coronal hole region. Two dipoles emerge one by
one. The negative element of the first dipole disappears due to the interaction
with the positive element of the second dipole. During this process, a jet and
a plasma eruption are observed. The opposite polarities of the second dipole
separate at first, and then cancel with each other, which is first reported in
a coronal hole. With the reduction of unsigned magnetic flux of the second
dipole from 9.8*10^20 Mx to 3.0*10^20 Mx in two days, 171 A brightness
decreases by 75% and coronal loops shrink obviously. At the cancellation sites,
the transverse fields are strong and point directly from the positive elements
to the negative ones, meanwhile Doppler red-shifts with an average velocity of
0.9 km s-1 are observed, comparable to the horizontal velocity (1.0 km s-1)
derived from the cancelling island motion. Several days later, the northeastern
part of the coronal hole, where the dipoles are located, appears as a quiet
region. These observations support the idea that the interaction between the
two dipoles is caused by flux reconnection, while the cancellation between the
opposite polarities of the second dipole is due to the submergence of original
loops. These results will help us to understand coronal hole evolution.
