The invention discloses a device for detecting green body strength of a nuclear fuel element. The device comprises a base, a vertical sliding mechanism, a clamping mechanism and a force measuring mechanism, wherein the vertical sliding mechanism is fixedly arranged on the base along a vertical direction; the clamping mechanism is transversely arranged along a horizontal direction; the clamping mechanism is provided with a mounting part and a clamping part used for clamping a green body; the mounting part of the clamping mechanism is connected with the vertical sliding mechanism in a sliding manner, so that the clamping mechanism can slide up and down along the vertical direction, and the vertical sliding mechanism can control the vertical sliding height of the clamping mechanism; the force measuring mechanism comprises a force measuring sensor and an impact plate which is transversely arranged along the horizontal direction; the impact plate is arranged on the base and positioned just under the clamping part of the clamping mechanism; and the force measuring sensor is mounted on the impact force to be used for detecting the impact force of the green body. The invention further provides a method for detecting the core block strength by using the device. The method is capable of effectively detecting external impact force stressed by a fuel core block, and has the advantages of small measuring error, stable and accurate data and the like, and is capable of greatly improving the detection efficiency.