The utility model discloses a transmission mechanism safety device of a strong-impact load stimulation safety case. The transmission mechanism safety device of the strong-impact load stimulation safety case is characterized in that the device is composed of a sliding shaft (1), a compressed spring (2), a fragile sheet (3), a shell (4) and a gland (5); the sliding shaft (1) is in clearance fit with an inner cavity of the shell (4); the compressed spring (2) is arranged below the sliding shaft (1) and the sliding shaft (1) slides in the axial direction in the inner cavity of the shell (4); the fragile sheet (3) is fixed to the top of the shell (4) and is compressed by the gland (5) and the sliding shaft (1) is packaged in the shell (4) through the gland (5); a hole is formed in the center of the gland (5) and the position of the hole corresponds to that of the sliding shaft (1). The transmission mechanism safety device is compact and simple in structure and can be conveniently installed in a transmission mechanism of a safety case door or a vault door, once a lock falls off due to explosion damage, the sliding shaft (1) of the safety device bounces out and serves as a tenon, the transmission mechanism still can be prevented from entering the unlocking state, and therefore the explosion damage resistant capacity of the case door can be effectively improved.