  In this work, we identify 734 ultracool dwarfs with a spectral type of M6 or
later, including one L0. Of this sample, 625 were studied spectroscopically for
the first time. All of these ultracool dwarfs are within 360~pc, with a
\textit{Gaia} G magnitude brighter than ~19.2 mag. By studying the spectra and
checking their stellar parameters (Teff, logg, and [FeH] derived with the
LAMOST pipeline, we found their cool red nature and their metallicity to be
consistent with the nature of Galactic thin-disk objects. Furthermore, 77 of
them show lithium absorption lines at 6708A, further indicating their young
ages and substellar nature. Kinematics obtained through LAMOST radial
velocities, along with the proper motion and parallax data from Gaia EDR3, also
suggest that the majority of our targets are thin-disk objects. Kinematic ages
were estimated through the relationship between the velocity dispersion and the
average age for a certain population. Moreover, we identified 35 binaries, with
6 of them reported as binaries for the first time.
