A composition which can be used as an organic water/oxygen barrier material, an OLED display device and manufacturing method thereof are disclosed. The composition includes: 15-25 wt % of parylene, 15-25 wt % of polyvinyl chloride, 5-15 wt % of acetone, 5-15 wt % of trichloroethylene, 10-20 wt % of polyvinyl acetate, 5-15 wt % of polyvinyl alcohol, 0-5 wt % of SiO2 nanoparticles, and 8-12 wt % of an organic solvent, wherein all weight percent values are based on the total weight of the composition. When a water/oxygen barrier layer fabricated by the composition is disposed between a luminescent layer of OLED and a light extraction layer, water vapor and oxygen gas can be prevented from entering the OLED luminescent layer, thereby prolonging the service life of the OLED luminescent layer.