  A study of the variability of the broad emission-line parameters of 3C390.3,
an active galaxy with the double-peaked emission-line profiles, is presented.
We give a detail analysis of variation in the broad Ha and Hb profiles, the
ratios, and the Balmer decrement of different line segments. Studying the
variability of the line profiles we explore the disk structure, that is assumed
to emit the broad double-peaked Ha and Hb emission lines. We divided the
observed spectra in two periods (before and after the outburst in 2002) and
analyzed separately the variation in these two periods. First we analyzed the
spectral emission-line profiles of Ha and Hb, measuring the peak positions.
Then, we divided lines into several segments, and we measured the line-segment
fluxes. The Balmer decrement variation for total Ha and Hb fluxes, as well as
for the line segments has been investigated and discussed. We modeled the line
parameters variation using an accretion disk model. We compared the variability
in the observed line parameters with the disk model predictions and found that
the variation in line profiles and in line segments corresponds to the emission
of a disk-like BLR. But, also there is probably one additional emission
component that contributes to the Ha and Hb line center. We found that the
variation in the line profiles is caused by the variation in the parameters of
the disk-like BLR, first of all in the inner (outer) radius which can well
explain the line parameter variations in the Period I. The Balmer decrement
across the line profile has a bell-like shape, and it is affected not only by
physical processes in the disk, but also by different emitting disk dimension
of the Ha and Hb line. The geometry of the BLR of 3C390.3 seems to be very
complex, and inflows/outflows might be present, but it is evident that the
broad line region with disk-like geometry has dominant emission.
