  The intensities of the hydrogen Balmer lines of solar-like stars are
investigated for stellar chromospheric activity by using the co-source spectral
data of the LAMOST Low-Resolution Spectroscopic Survey (LRS) and
Medium-Resolution Spectroscopic Survey (MRS). The Balmer H$\alpha$, H$\beta$,
H$\gamma$, and H$\delta$ lines in the LRS data and the H$\alpha$ line in the
MRS data are analyzed. The absolute flux indexes, defined as the ratios of the
absolute fluxes at the centers of the Balmer lines to the stellar bolometric
flux, are employed to indicate the intensity magnitudes of the Balmer lines in
response to stellar activity. The H$\alpha$ indexes derived from the LRS data
and the MRS data, respectively, are calibrated to be quantitatively consistent
with each other. It is found that, as the H$\alpha$ index increases, the
H$\beta$, H$\gamma$, and H$\delta$ indexes first present trend of increasing
and then decreasing, and finally increase synchronously with the H$\alpha$
index. The distributions of the Balmer line indexes also reveal the three
distinct stages of stellar activity (normal stage, intense stage, and extremely
intense stage), in which the extremely intense stage is characterized by the
synchronous growth of the indexes of the four Balmer lines. The different
behaviors of the H$\beta$, H$\gamma$, and H$\delta$ lines from that of the
H$\alpha$ line can be interpreted by the different mechanisms by which the
line-core intensities are formed, and the three distinct activity stages imply
the very different magnetic field environments and physical conditions of
solar-like stars.
