  Gamma-ray bursts (GRBs) are among the most powerful explosive events in the
universe. LHAASO recently observed the most luminous one: GRB 221009A, and
unveiled its TeV light curve. The light curve exhibits a distinct jet break at
around 670 seconds, enabling the derivation of the viewing angle based on the
smoothness of the jet break. We constructed two models with or without
considering the high-latitude radiation, where the viewing angle was treated as
a free parameter, to fit the TeV light curve. We obtained the viewing angles
being 9.4 $\times 10^{-4}$ radians and 5.9 $\times 10^{-3}$ radians,
respectively. These values closely resemble an on-axis scenario, given the
opening angle is 1.4 $\times 10^{-2}$ radians.
