  The tiny modification of dispersion relation induced by Lorentz violation
(LV) is an essential issue in quantum gravity (QG) theories, which can be
magnified into significant effects when dealing with astrophysical observations
at high energy and long propagation distance. LV would lead to photon decay at
high energies, therefore, observations of high-energy photons could constrain
LV or even QG theories. The Large High Altitude Air Shower Observatory (LHAASO)
is the most sensitive gamma-array instrument currently operating above 100 TeV.
Recently, LHAASO reported the detection of 12 sources above 100 TeV with
maximum photon energy exceeding 1 PeV. According to these observations, the
most stringent restriction is achieved in this paper, i.e., limiting the LV
energy scale to $1.7\times10^{33} $ eV, which is over 139,000 times that of the
Planck energy and achieve an improvement of about 1.9 orders of magnitude over
previous limits.
