We identify 734 ultracool dwarfs having spectral type M6 or later including one L0, of which, 625 are having spectral observation for the first time with LAMOST. All these ultracool dwarfs are within 360 pc, with the Gaia G magnitude brighter than ~19.2mag. Studying the spectra and checking their stellar parameters (Teff, logg and [M/H]) derived with the LAMOST pipeline, we found their cool red nature and their metallicity consistent with being Galaxy thin disk objects. Furthermore, 77 of them show lithium absorption line at 6708{AA} indicating their young ages and substellar nature. Kinematics obtained through LAMOST radial velocities combining with the proper motion and parallax from Gaia EDR3, also suggest the majority of our targets are thin disk objects. Kinematic ages are estimated through the relationship between the velocity dispersion and the average age for a certain population. Moreover, 35 binaries are identified, among which 6 are reported as binaries for the first time.

Cone search capability for table J/A+A/660/A38/table1 (The ultracool dwarfs)

Cone search capability for table J/A+A/660/A38/table2 (Radial velocity and atmosphere parameters in LDR7)

Cone search capability for table J/A+A/660/A38/table3 (Kinematic parameters)