  We perform a NLO QCD analysis of the combined SLAC-BCDMS-NMC-E665-H1-ZEUS
data on inclusive deep inelastic cross section. Particular attention was paid
to the extraction of strong coupling constant $\alpha_s$ and high twist (HT)
contribution to the structure functions $F_2$ and $F_L$. It was shown that at
small and moderate x there is a visible dependence of the extracted values of
HT contribution to $F_2$ on the QCD renormalization scale, which indicates that
in this region extracted HT can absorb NNLO QCD corrections. At larger x the
dependence of HT on the renormalization scale is negligible and the influence
of NNLO correction on their values should be less significant. The value of
$\alpha_s(M_Z)=0.1159\pm0.0031$ (total) is obtained, where the error includes
statistical, systematical and theoretical uncertainties.
