  We propose a method to search for stellar-mass black hole (BH) candidates
with giant companions from spectroscopic observations. Based on the stellar
spectra of LAMOST Data Release 6, we obtain a sample of seven giants in
binaries with large radial velocity variation $\Delta V_R > 80~{\rm
km~s^{-1}}$. With the effective temperature, surface gravity, and metallicity
provided by LAMOST, and the parallax given by {\it Gaia}, we can estimate the
mass and radius of the giant, and therefore evaluate the possible mass of the
optically invisible star in the binary. We show that the sources in our sample
are potential BH candidates, and are worthy of dynamical measurement by further
spectroscopic observations. Our method may be particularly valid for the
selection of BH candidates in binaries with unknown orbital periods.
