The invention provides a nickel oxide thin film, a preparation method thereof, functional material, a manufacturing method of a thin film structure and an electroluminescent device. The nickel oxide thin film comprises a nickel oxide film layer and organic molecules with electron withdrawing groups. The organic molecules are connected to the surface of the nickel oxide film layer. Chemical bond stable connection is formed between the organic molecules and hydroxyl radical free radicals on the surface of the nickel oxide thin film by use of the electron withdrawing groups. Due to the existenceof the organic molecules with the electron withdrawing groups, a reverse nickel oxide electric field is established on the surface of the nickel oxide, so the surface work function of the nickel oxidethin film is improved. When the nickel oxide thin film with the high surface work function is applied to a QLED device and an OLED device, the hole injection rate is improved, use of PEDOT:PSS whichwill damage the devices can be avoided and performance and stability of the devices are improved.