The invention discloses a calibration device for a nuclear magnetic resonance well logger, which comprises a circulation system, a shielding dial drum and a lithologic medium placing board, wherein the circulation system consists of a mixing vessel, a vacuum valve and a Faraday dial drum; the Faraday dial drum is provided with an instrument outer cylinder which is used for placing a detecting instrument and a corresponding probe; the shielding dial drum is sleeved outside the instrument outer cylinder and used for circulating flow of a calibration solution; the lithologic medium placing boardis arranged inside the shielding dial drum and used for placing solid lithologic media; a skylight for placing and taking the solid lithologic media is also arranged on the shielding dial drum; and askylight cover is arranged on the skylight. The calibration device for the nuclear magnetic resonance well logger not only effectively reduces the volume of the calibration device and shields interference of an external electromagnetic field but also can conveniently and flexibly replace the lithologic media, accurately calibrate the investigation depth and the sensitivity on the lithologic mediawith various porosities, and provide accurate scale data for the nuclear magnetic resonance well logger.