The invention discloses a perovskite photoelectric detector based on a DNT-PH composite hole transport layer and a preparation method thereof. The photoelectric detector is used for industrial automation, aerospace, fire early warning and other devices. The invention belongs to the technical field of photoelectric detection, and the problems that a traditional hole transport layer material Spiro-OMeTAD is low in migration rate, poor in device stability and short in service life are solved. The photoelectric detector sequentially comprises a transparent substrate, a conductive cathode, an electron transport layer, a perovskite photoactive layer, a composite hole transport layer and a metal anode from bottom to top, the composite hole transport layer is of a double-layer structure, a lower-layer film is made of Spiro-OMeTAD, and an upper-layer film is made of DNT-PH small molecules. The DNT-PH has a relatively high homo energy level; the charge transfer between the hole transport layer and the electrode can be promoted; meanwhile, the recombination of carriers is inhibited in a dark state such that the photocurrent is improved, the dark current is greatly reduced, DNT-PH covers the surface of the Spiro-OMeTAD, the corrosion of water and oxygen to the device can be effectively reduced, the stability is further enhanced, and the stability and the service life of the device are greatly improved.