  We use LAMOST DR4 M giants combined with Gaia DR2 proper motions and ALLWISE
photometry to obtain an extremely pure sample of Sagittarius (Sgr) stream
stars. Using TiO5 and CaH spectral indices as an indicator, we selected out a
large sample of M giant stars from M dwarf stars in LAMOST DR4 spectra.
Considering the position, distance, proper motion and the angular momentum
distribution, we obtained 164 pure Sgr stream stars. We find that the trailing
arm has higher energy than the leading arm in same angular momentum. The
trailing arm we detected extends to a heliocentric distance of $\sim 130$ kpc
at $\tilde\Lambda_{\odot}\sim 170^{\circ}$, which is consistent with the
feature found in RR Lyrae in \citet{sgr2017}. Both of these detections of Sgr,
in M giants and in RR Lyrae, imply that the Sgr stream may contain multiple
stellar populations with a broad metallicity range.
