An apparatus for testing strength of a corner portion of an object includes a support platform, an installing mechanism on the platform, a force gauge, a driving mechanism connected to the slidable plate to move the slidable plate, a clamp mechanism for clamping the object in a fixed position, and a push-pull mechanism. The installing mechanism includes two opposite rail plates mounted to the platform, and a slidable plate slidably mounted between the rail plates. The force gauge is fixed to the slidable plate. The push-pull mechanism is connected to the force gauge to be pushed or pulled by the force gauge. The push-pull mechanism comprises two forcing posts to respectively abut against two sides of the object at the corner portion, thereby exerting push or pull force on the two sides of the corner portion to test strength of the corner portion.