The invention discloses an anti-turnover protection device for a car door sub-assembly table. The anti-turnover protection device comprises a car door sub-assembly table installing base, and is characterized in that an L-shaped barrier rack is movably connected to the outer end of the installing base, a supporting locking plate is movably connected to the bottom of the installing base, and when an L-shaped bottom plate of the L-shaped barrier rack is adjusted to be flush with the installing base, the supporting locking plate can be adjusted to be located below the L-shaped barrier rack and connected with the L-shaped barrier rack in an abutting mode. As is shown in practice, the protection device can effectively avoid the situations that if car doors on the sub-assembly table turn over on one side due to sudden external force or misoperation or the like during modular production, operators are injured and the car doors are collided to be damaged.