A photodetector, a preparation method for a photodetector, a photodetector array and a photodetection terminal. The photodetector comprises a substrate (11) and an optical resonant cavity (10) formed on the substrate (11). The optical resonant cavity (10) may comprise: a light absorption layer (13) having a light-entrance outer surface and a bottom outer surface which are opposite to each other, and an outer sidewall located between the light-entrance surface and the bottom surface; a light-strap structural layer (14) covering the light-entrance surface; and a light-reflection structural layer (12) covering the bottom outer surface and/or the outer sidewall of the light absorption layer (13), wherein the light-reflection structural layer (12) is configured to reflect external light entering the optical resonant cavity (10) by means of the light-trap structural layer (14) to increase a light propagation distance of the external light in the light absorption layer (13), thereby effectively improving the photon absorption efficiency of the photodetector.