An embodiment auto sliding ramp for a vehicle includes a drive motor, a clutch rod including a clutch body slidably inserted inside the drive motor and a clutch gear mounted on the clutch body, a motor clutch connecting the drive motor and the clutch rod, a ramp drive unit configured to drive the ramp according to its rotation, a main drive including a drive gear engaged with the ramp drive unit and a drive shaft connected to the drive gear and configured to manually rotate the drive gear, and a clutch operation part configured to disengage the motor clutch by pushing the clutch rod.