The angular and wavelength selectivities of band gaps of holographic photonic crystals were calculated using transfer matrix method for different polarizations.It showed that the width of the band gaps for P-polarization is narrower than that for S-polarization. About the angular selectivity, the changing trends for different polarizations are the same, but with different degree of variations. About the wavelength selectivity, the changing trends for different polarizations are in an opposite way. A \!general Brewster's angle\" is introduced. The theoretical analysis shows that when a beam incident on a photonic crystal just at the general Brewster's angle\", the forbidden band of S-polarization will still exist as it is, while the forbidden band of P-polarization will vanish. Therefore , a \!defect mode\" can be obtained in the forbidden band of S-polarization by i lluminating the photonic crystal with P-polarization beam at the \!general Brews ter's angle\". The experimental results for verifying the theoretical calculatio ns were given.