The invention provides a landing gear. The landing gear comprises a landing gear outer cylinder (1) and a landing gear tyre (3). The landing gear is characterized by further comprising a detecting device (2), wherein a laser ranging device is used for the detecting device (2) ; the detecting device (2) is mounted on the landing gear outer cylinder (1) and positioned above the landing gear tyre (3); laser rays emitted by the detecting device (2) are parallel to the peripheral end surfaces of both sides of the landing gear tyre (3). When the landing gear tyre (3) does not touch down, the laser rays emitted by the detecting device (2) are not shielded by the landing gear tyre (3); when the landing gear tyre (3) touches down, the laser rays emitted by the detecting device (2) are shielded by the landing gear tyre (3).