The formulas of reflection coefficient, transmission coefficient, electric and magnetic fields of onedimensional sinc function photonic crystals are deduced by the transfer matrix method on the condition of oblique incidence of the transverse magnetic (TM) wave. On this basis, a heterojunction composed of two semifinite photonic crystals is analyzed in detail. It is found that the semi- infinite photonic crystals on both sides of the heterostructure are equivalent to the negative permittivity materials or the negative permeability materials. Under the matching conditions, Tamm states emerge. By reducing the ratio of the optical thickness of the two dielectric layers, the first bandgap of TM or TE wave is significantly widened, and blueshift occurs for the position of the first bandgap. When refractive indices of the two media are increased in the same magnification, width of the first bandgap of TM or TE wave changes in the opposite directions, the former is gradually widened, the latter is narrowed, and redshift occurs for the position of the first bandgap. Transmission spectrum of the heterojunction is also significantly affected by the cycle number and angle of incidence.