An optical simulation including reflection and refraction is used to simulate the light illumination intensity of gallium nitride (GaN)-based light-emitting diodes (LEDs) on varied patterned sapphire substrates (PSS) with different slanted angles and fill factors (f). It is found that a micro pyramid array with a slanted angle from 25 degrees to 60 degrees is able to effectively improve illumination intensity which reaches to summit as the slanted angle is around 33 degrees. And illumination intensity enhances monotonously as increases. In addition to the mentioned work, epitaxial growth of GaN-LEDs on PSS is investigated for comparison. The output power of GaN-LEDs on PSS increases with simulated light illumination intensity increasing. The experimental results prove the simulation.