The resonance mechanism sets up a resonant cavity model of 1D half infinite period photonic crystal, and takes advantage of resonance conditions to infer the analytical formulas of the wavelength deduced by the total reflection tunnel effect. The physical mechanism of the total reflection tunnel effect of 1D half infinite period photonic crystal is explained. By using the formulas, the wavelength changes related to order number, thickness of resonant cavity, as well as the incident angle, are analyzed and the change law of the total reflection tunnel effect is explained successfully. Resonance theory results and dispersion method results are compared and their results are the same.