The present disclosure relates to a manufacturing method of flexible OLED. The method includes: S1: forming an anode and a hole transport layer on substrate being stacked in sequence, and forming a cathode and an electron transport layer being stacked in sequence; S2: applying an acidification process to a surface of the electron transport layer to obtain a cover assembly, and applying the acidification process to a surface of the hole transport layer; S3: forming a stopper chamber on the hole transport layer after being applied with the acidification process; S4: injecting liquid luminescent material into the stopper chamber to form a light emitting layer so as to obtain the substrate; S5: clasping the cover assembly on the substrate, and configuring the electron transport layer being applied with the acidification process to face toward the light emitting layer so as to obtain the flexible OLED.