  We study the classification and composite spectra of galaxy in the fourth
data release (DR4) of the Large Sky Area Multi-Object Fiber Spectroscopic
Telescope (LAMOST). We select 40,182 spectra of galaxies from LAMOST DR4, which
have photometric in- formation but no spectroscopic observations in the Sloan
Digital Sky Survey(SDSS). These newly observed spectra are re-calibrated and
classified into six classes, i.e. pas- sive, H{\alpha}-weak, star-forming,
composite, LINER and Seyfert using the line intensity (H\b{eta},
[OIII]{\lambda}5007, H{\alpha} and [NII]{\lambda}6585). We also study the
correlation between spectral classes and morphological types through three
parameters: concentration index, (u - r) color, and D4000n index. We calculate
composite spectra of high signal-to-noise ra- tio(S/N) for six spectral
classes, and using these composites we pick out some features that can
differentiate the classes effectively, including H\b{eta}, Fe5015, H{\gamma}A,
HK, and Mg2 band etc. In addition, we compare our composite spectra with the
SDSS ones and analyse their difference. A galaxy catalogue of 40,182 newly
observed spectra (36,601 targets) and the composite spectra of the six classes
are available online.
