A radiation detector assembly and a method of manufacturing the same are provided. The radiation detector assembly includes a base and an outer encapsulation layer. The base includes a scintillator having a light-entering surface and a light-exiting surface on both ends thereof, respectively; a reflection layer provided on the light-entering surface and an outer peripheral surface of the scintillator; a photosensor comprising a photosensitive surface and an encapsulation housing, the photosensitive surface is coupled to the light-exiting surface via an optical adhesive; and an inner encapsulation layer adhered to an outer surface of the reflection layer and hermetically encapsulates a coupling portion where the scintillator and the photosensor connected with each other. The outer encapsulation layer is provided on the outer surface of the base.