The invention discloses a parking braking mechanism, a parking braking system, an automatic transmission and an automobile. The parking braking mechanism is used for locking a locking gear and comprises a detent, a parking sliding block and a movable pressing pin, the parking sliding block can push the detent to move, so that the detent locks the locking gear; the movable pressing pin can move toa locking position and an unlocking position, when the pressing pin is located at the locking position, the pressing pin can clamp the parking sliding block, and when the pressing pin is located at the unlocking position, the pressing pin relieves clamping on the parking sliding block. Therefore, when the locking gear is required to be unlocked, the pressing pin moves to the unlocking position, the pressing pin relieves clamping on the parking sliding block, by this time, only a small action force is required to be applied to the parking sliding block, the parking sliding block and the detentcan be separated, unlocking is finished, therefore, a driving motor with relatively small torque is only required, and the cost is reduced accordingly.