The utility model discloses an angular displacement sensor especially is suitable for absorption on the beam -pumping unit's of petroleum industry walking beam, test oil well indicator card, easy to assemble and dismantlement. This sensor includes the casing, is equipped with signal line clearing hole, the downthehole signal line fixed head that is equipped with on the casing, passes through the screw fixation in casing one side with the strong magnet, and the screw mounting hole of strong magnet is the counter bore. The utility model discloses reduced the degree of difficulty of maintaining of sensor, after the ready work in ground, the dismouting of whole sensor can be accomplished to single one hand among the high altitude construction, and the another hand can carry out self -protection. Reduce constructor's potential safety hazard, shortened simultaneously by a wide margin and stopped the well time, do not needed special technical ability and special equipment's cooperation construction. The dismantlement can be accomplished in about 1 minute by shortening to in original 20 minutes to the dismouting time, had reduced the influence to oil well production. Because easy dismounting has avoided the equipment among the oil well operation to damage, has reduced the input cost.