  We analyze spectroscopic and photometric observations of the eclipsing polar
BS Tri. The polar's light curve shape variations can be interpreted by changing
contributions of the accretion stream to the integral radiation of the system.
Based on the radial velocity curves of the irradiated part of the secondary, we
refine the masses of the system components, $M_1 = 0.60 \pm 0.04 M_{\odot}$,
$M_2 \approx 0.12 M_{\odot}$, and the orbital inclination, $i=85\pm
0.5^{\circ}$. The polar's spectra reveal cyclotron harmonics forming in an
accretion spot with a magnetic field strength of $B=22.7 \pm 0.4$ MG and an
average temperature of $T \sim 10$ keV. In addition to the cyclotron harmonics,
the BS Tri spectra contain Zeeman components of H$\alpha$ line, which are
probably formed in the cool halo near the accretion spot. The orientation of
the magnetic dipole and the coordinates of the accretion spot are estimated by
modeling the light curves of the polar. We show that for a satisfactory
description of the BS~Tri light curves we have to take into account the
variability of the spot's optical depth along the line of sight. Doppler maps
of BS Tri show a part of the accretion stream with a trajectory close to
ballistic near the Lagrange point L$_1$, and another part of the stream moving
along the magnetic field lines. The estimate of the stagnation region position
found from the Doppler tomograms is consistent with the photometric estimates
of the accretion spot position.
