A transparent top electrode composite film for organic optoelectronic devices includes a substrate, an MoOx film layer coated on the substrate, a doped Ag-based film layer coated on the MoOx film layer and an HfOx film layer coated on the doped Ag-based film layer. A preparation method of the transparent top electrode composite film, which is achieved under vacuum and low temperature, includes steps of (A) depositing an MoOx film layer on a substrate through thermal evaporation process or electron beam evaporation process without heating the substrate; (B) depositing a doped Ag-based film layer on the MoOx film layer through sputtering process or evaporation process; and (C) depositing an HfOx film layer on the doped Ag-based film layer through reactive sputtering process, thereby obtaining the transparent top electrode composite film. The composite film is able to be used as a top electrode material for organic optoelectronic devices.