The invention relates to an embedded joint meter for detecting the width variation of cracks or structrual joint (deep) in concrete or rock and soil structure object, and detection method thereof. The joint meter comprises a sensor sheath and a displacement sensor disposed in the sensor sheath; hole positioning devices are connected on both ends of the sensor sheath through extension bars. The beneficial effect of the invention is that: 1, it can detect the width variation of cracks or structrual joint (deep) in concrete or rock and soil structure object effectively and accurately for a long term, grasp the width variation case of cracks or joints at any moment, provide information to the safe operation and management of engineering building, and provide technical support to engineering building safety estimation; 2, it can be embedded into crack directly when used, achieves the advantages of simple structure, reasonable arrangement, convenient and firm positioning, high detection precision, reliable operation performance, convenient using and high practicability, and for installed in a hole, instrument can be protected easily, need not maintenance and has a long service life; 3, the detection method is direct and convenient.