The invention discloses a clamping device and a cradle head. The clamping device comprises a clamping part and a connecting part. The clamping part comprises a substrate and a bottom plate. The substrate is arranged on the bottom plate. The clamping part is rotatably connected with the connecting part through the bottom plate. A clamping part is arranged on the substrate. A rack, at least one gear and an elastic part are arranged below the substrate. The rack moves to drive the gears to rotate so as to enable the clamping part to expand. The two ends of the elastic part are connected to the rack and the substrate correspondingly. Through the technical scheme, the clamping interval of the clamping part can be adjusted flexibly so as to adapt to various kinds of photographing devices; and the clamping device can clamp the photographing device firmly to prevent the photographing device from falling off.