  We study the commensurately-tilted bilayer graphene in the tight-binding
model with changing the interlayer distance, which can be tuned by pressure. We
find that at the commensurately-tilted bilayer graphene with moderate rotating
angles, when the energy gap at K point is not negligible, the other Dirac
points within the upper two bands move along the $\Gamma$-K-M line in the
bilayer Brillouzone, when the interlayer distance is changed. The velocity at K
point becomes zero due to the merging of the four Dirac points within upper two
bands. This mechanism of zero velocity at K point is expected to be the origin
of the magic angle with flat band at ambient pressure, at which the upper two
bands are almost degenerate and the band gap at K can be neglected.
