A linear actuator, comprising: a first sleeve, a second sleeve, a rotary screw, a transmission nut, and a driving motor, the driving motor activating the rotary screw to rotate, the rotating rotary screw driving the transmission nut to move axially, and movement of the transmission nut causing the first sleeve and the second sleeve to extend and retract relative to each other, wherein a self-locking apparatus is mounted on the rotary screw; the self-locking apparatus comprising: a one-way bearing and a friction collar, wherein the one-way bearing comprises an inner race and an outer race, the inner race being sleeved to a rotary screw of the linear actuator, the friction collar being connected to the outer race; wherein the self-locking apparatus further comprises a friction member fitted with the friction collar, such that when the rotary screw rotates forwardly, the outer race does not rotate; and when the rotary screw rotates reversely, the outer race, the inner race, and the friction collar rotate synchronously, such that friction is produced by contacting between the friction collar and the friction member, wherein the friction collar is sleeved over the outer race, and a plane bearing is further mounted on the rotary screw, wherein the linear actuator further comprises a support base, an axial direction of the support base being distant from the plane bearing; the friction member comprises a friction outer race mounted in the support base, the friction outer race being sleeved outside the friction collar, such that friction is produced by contacting between the friction outer race and a circumferential side portion of the friction collar, characterized in that the plane bearing and the friction member are located at two different axial sides of the friction collar and in that a circumferential sidewall of the friction collar has an outer conical surface, the outer conical surface being gradually shrunk towards a side distant from the plane bearing, an inner sidewall of the friction outer race has an inner conical surface adapted to the outer conical surface; or, a circumferential side surface of the friction collar is a stepped surface, the inner sidewall of the friction outer race being adapted to the stepped surface. the self-locking apparatus comprising: a one-way bearing and a friction collar, wherein the one-way bearing comprises an inner race and an outer race, the inner race being sleeved to a rotary screw of the linear actuator, the friction collar being connected to the outer race; wherein the self-locking apparatus further comprises a friction member fitted with the friction collar, such that when the rotary screw rotates forwardly, the outer race does not rotate; and when the rotary screw rotates reversely, the outer race, the inner race, and the friction collar rotate synchronously, such that friction is produced by contacting between the friction collar and the friction member, wherein the friction collar is sleeved over the outer race, and a plane bearing is further mounted on the rotary screw, wherein the linear actuator further comprises a support base, an axial direction of the support base being distant from the plane bearing; the friction member comprises a friction outer race mounted in the support base, the friction outer race being sleeved outside the friction collar, such that friction is produced by contacting between the friction outer race and a circumferential side portion of the friction collar, characterized in that the plane bearing and the friction member are located at two different axial sides of the friction collar and in that a circumferential sidewall of the friction collar has an outer conical surface, the outer conical surface being gradually shrunk towards a side distant from the plane bearing, an inner sidewall of the friction outer race has an inner conical surface adapted to the outer conical surface; or, a circumferential side surface of the friction collar is a stepped surface, the inner sidewall of the friction outer race being adapted to the stepped surface.