The wavelength and angle dependent optical transmission of two-dimensional photonic crystal slab are calculated using rigorous coupled wave analysis (RCWA) method. The relationship between guided resonance of spectrum and the band structure of two-dimensional photonic crystal slab is investigated. Based on InP material photonic crystal slab, angle resolved and wavelength resolved optical switches are designed utilizing the characterization of low transmission and high quality factor of guided resonance. These switches operate at the wavelength of 1550 nm. It shows that the quality factor of guided resonance mode in the transmission spectrum can reach 105, and achieve an on-off contrast of nearly 100% with the nonlinear refractive index change of 10-4. As the signal light and pump light couple with the guided resonance modes of photonic crystal slab respectively, the field intensity of pump light is enhanced, and the pump energy is reduced to only 184 fJ. To our knowledge, this is the lowest energy needed for optical switcher.