  With more than 150 blank sky observations at high Galactic latitude, we make
a systematic study to the background of the Low Energy Telescope (LE) of the
Hard X-ray Modulation Telescope (dubbed as Insight-HXMT). Both the on-ground
simulation and the in-orbit observation indicate that the background spectrum
mainly has two components. One is the particle background that dominates above
7 keV and its spectral shape is consistent in every geographical locations.
Another is the diffuse X-ray background that dominates below 7 keV and has a
stable spectrum less dependent of the sky region. The particle background
spectral shape can be obtained from the blind detector data of all the blank
sky observations, and the particle background intensity can be measured by the
blind detector at 10-12.5 keV. The diffuse X-ray background in the high
Galactic latitude can also be obtained from the blank sky spectra after
subtracting the particle background. Based on these characteristics, we develop
the background model for both the spectrum and the light curve. The systematic
error for the background spectrum is investigated with different exposures
(T_exp). For the spectrum with T_exp=1 ks, the average systematic errors in 1-7
keV and 1-10 keV are 4.2% and 3.7%, respectively. We also perform the
systematic error analyses of the background light curves with different energy
bands and time bins. The results show that the systematic errors for the light
curves with different time bins are <8% in 1-10 keV.
