Abstract: As the transmission gear box on the top of the blast furnace works permanently under the heavy load, high temperature, dust and blast furnace gas, its working condition is very severe. In order to avoid its sudden malfunction, it was detected on its vibration and the grease during the working period. Furthermore, the data were analyzed using the frequency spectrum and action spectrum methods. Finally the test on the material of the failure parts was made after the gear box was disassembled. The above research manifested that the stop of most transmission gear box on the top of the blast furnace was caused by the lock of the cross-rolling bearing, and one of the reasons of the lock was the damage of the cage. The rolling elements in the bearing disturbed each other after the damage of the cage, and the moving condition of some changed from rolling to sliding. As a result, the rolling elements pressed each other and damaged, finally the rotation of gear ring was impeded and locked.