Taking into account the Stark structure of optical spectrum of the impurity ion, the theoretical study of spectroscopic properties of LiNbO3:Tm3+ crystal in the wavelength range of 1650–1970 nm was carried out. The wave functions of the Stark sublevels of both ground 3H6 and the first excited 3F4 manifolds of the Tm3+ ion were constructed in the LSJM-representation, the line strengths induced by indirect electric-dipole transitions were calculated, and the main spectroscopic characteristics of emission and absorption spectra of impurity ion were determined.