The present invention discloses a blue light quantum dot film electroluminescent device and a preparation method thereof. The blue light quantum dot film electroluminescent device comprises a substrate, an anode, a hole injection layer, a hole transport layer, a blue light quantum dot luminescent layer, a blue light energy transfer layer, an electronic transmission layer, an electronic injection layer and a cathode which are laminated orderly. The thickness of the blue light quantum dot luminescent layer is between 8 nm and 15 nm, and the thickness of the blue light energy transfer layer is between 0.2 nm and 2.2 nm. The blue light quantum dot film electroluminescent device firstly adopts the blue light quantum dot luminescent layer of which the thickness is between 8 nm and 15 nm, so that the blue light quantum dot luminescent layer forms an incompletely continuous film, and a hole can partially penetrate the blue light quantum dot luminescent layer rather than accumulating excessively on the interfaces of the blue light quantum dot luminescent layer and the hole transport layer. Excitons reach the blue light quantum dot luminescent layer to enable the blue light quantum dot luminescent layer to emit light after the blue light energy transfer layer is formed and in an energy transfer manner, thereby solving the problem that the hole injection barrier of the blue light quantum dot film electroluminescent device is higher.