  In this paper, we report the discovery of a new late-B type unbound
hyper-runaway star (LAMOST-HVS4) from the LAMOST spectroscopic surveys.
According to its atmospheric parameters, it is either a B-type main sequence
(MS) star or a blue horizontal branch (BHB) star. Its Galactocentric distance
and velocity are 30.3 +/- 1.6 kpc and 586 +/- 7 km/s if it is an MS star, and
they are 13.2 +/- 3.7 kpc and 590 +/- 7 km/s if a BHB star. We track its
trajectories back, and find that the trajectories intersect with the Galactic
disk and the Galactic center lies outside of the intersection region at the 3
sigma confidence level. We investigate a number of mechanisms that could be
responsible for the ejection of the star, and find that it is probably ejected
from the Galactic disk by supernova explosion or multiple-body interactions in
dense young stellar clusters.
