  We analyze a time series of optical spectra of SN 1993J-like supernova
1996cb, from 14 days before maximum to 86 days after that, with a parameterized
supernova synthetic-spectrum code SYNOW. Detailed line identification are made
through fitting the synthetic spectra to observed ones. The derived
photospheric velocity, decreasing from 11,000 km/s to 3,000 km/s, gives a rough
estimate of the ratio of explosion kinetic energy to ejecta mass, i.e. E/M_ej
\sim 0.2-0.5 \times 10^51 ergs / M_ej(M_\sun). We find that the minimum
velocity of hydrogen is about 10,000 km/s, which suggests a small hydrogen
envelope mass of \sim 0.02-0.1 M_ej, or 0.1-0.2 M_\sun if E is assumed 1 \times
10^51 ergs. A possible Ni II absorption feature near 4000 \AA is identified
throughout the epochs studied here and is most likely produced by primordial
nickel. Unambiguous Co II features emerge from 16 days after maximum onward,
which suggests that freshly synthesized radioactive material has been mixed
outward to a velocity of at least 7,000 km/s as a result of hydrodynamical
instabilities. Although our synthetic spectra show that the bulk of the
blueshift of [O I] 5577 net emission, as large as \sim 70 \AA at 9 days after
maximum, is attributed to line blending, a still considerable residual \sim 20
\AA remains till the late phase. It may be evidence of clumpy or large-scale
asymmetric nature of oxygen emission region.
