Several methods to improve the light extraction efficiency of GaN light emitting diode (LED) are introduced. These methods include fabricating a GaN LED with photonic crystal and other structures, such as microcavity, omni-directional reflector, patterned sapphire substrate, AlGaN confining layer, and embedded photonic crystals. These structures would change the optical design of LEDs and modulate the distribution of guide modes in LEDs to improve the light extraction efficiency. From experiment demonstration and theoretical analysis of five specially designed LEDs, it is found that the characteristics of LED light emission are modulated and the LED light emission intensity is enhanced considerably compared with conventional LEDs.