Based on the geometrical optics model,the expression of flexible organic light emitting devices (FOLED)′s out-coupling efficiency was presented. The influence of substrate curvature and its thickness,and organic layer′s refractive index on the performance of the FOLED′s out-coupling efficiency was studied,and the variation of out-coupling efficiency between FOLED and plane organic light emitting display (OLED) are contrasted as well. The result shows that:the out-coupling efficiency is enhanced with increased substrate curvature and its thickness,but is reduced with increased organic layer′s refractive index for outcurved substrate. The out-coupling efficiency is reduced with increased substrate curvature and thickness,and is also reduced with increased organic layer′s refractive index for incurvated substrate. The out-coupling efficiency of OLED is reduced with increased organic layer′s refractive index.