The invention provides a flexible perovskite solar cell and a preparation method thereof. A structure of the flexible perovskite solar cell provided by the invention comprises an electron-transporting layer, a compounded light absorption layer, a hole-transporting layer and a counter electrode in sequence on a flexible substrate; the electron-transporting layer is black phosphorus; and the light absorption layer is a black phosphorus/inorganic perovskite structure compounded light absorption layer. The invention further provides the preparation method of the solar cell. In the flexible perovskite solar cell and the preparation method thereof provided by the invention, compared with a metal oxide semiconductor taken as the electron-transporting layer, the electron-transporting layer composed of the black phosphorus can be thermally treated under the condition of a lower temperature (less than 150 DEG C), and simultaneously has more excellent electron transport performance and is suitable for being applied to a flexible device; and in addition, by adopting the black phosphorus/inorganic perovskite structure compounded light absorption layer, the absorption spectrum of the solar cell can be expanded to a visible-infrared band, and the photoelectric conversion efficiency and the stability of the perovskite solar cell are improved.