The invention discloses a door locking knife for preventing forced opening of an elevator car door. The door locking knife comprises a door knife rocker, a door knife back plate, a door knife upper connecting rod, a left knife arm, a right knife arm, a knife arm lower connecting rod, a latch hook assembly and a unlocking mechanism; and the door knife upper connecting rod, the left knife arm, the knife arm lower connecting rod and the right knife arm are connected in sequence to form a parallelogram linkage mechanism. An avoiding groove is formed in the door knife back plate; the unlocking mechanism includes a unlocking plate, and a unlocking plate linkage mechanism capable of realizing linkage of the unlocking plate with the parallelogram linkage mechanism; the unlocking plate is provided with an unlocking plate trigger body; the latch hook assembly includes a latch hook body, and a latch hook trigger body connected with the latch hook body; and the unlocking plate trigger body and the latch hook trigger body contact in linkage of the parallelogram linkage mechanism to generate tangent motion so as to force the latch hook body to rotate. The door locking knife is reliable in action, simple in structure debugging and installation and low in failure rate.