Recently, the plasma Bragg gratings induced by two intersecting laser pulses has been predicted theoretically. The dispersion relation of uniform plasma gratings under the oblique incidence of a light wave is investigated with the transfer-matrix method and the coupled-mode theory. Both approaches show that such plasma gratings exhibit a photonic band gap, near which strong dispersion appears. The photonic band gap has different polarization characteristics when the light wave is obliquely incident on the plasma grating. With the increase of the incident angle, the band gap for an S-polarized wave increases gradually, while that for a P-polarized wave decreases first rapidly, then vanishes when it approaches the Brewster angle, and finally becomes wide with the further increase of the incident angle. Since the plasma grating has an ultrabroad photonic band gap and can support an ultrahigh damage threshold of incident light waves, it has the potential to be a novel photonic device to manipulate extremely intense laser pulses.