We demonstrate by finite-difference time-domain simulations that a one-dimensional (1D) photonic crystal (PC) structure between glass substrate and indium tin oxide layer can improve the light extraction efficiency of organic light-emitting diodes. The extraction efficiency depends on the emitters' positions varying laterally in a unit cell of PC. The highest efficiency is obtained when the emitters are under higher refractive index strips. Efficiency decreases when the emitters shift to lower refractive index strips. Simulations for both transverse magnetic and transverse electric modes indicate that when emitters are close to the middle of the higher refractive index strips, the guided wave transmits with less divergence and inhibited reflection because of the guiding effect of higher refractive index strips. A modified method that considers the position effects is proposed to calculate the extraction efficiency more precisely.