The DTH hammer drill bit used for casing while drilling is the main tool of rock breaking and it is one of the important components of air reverse circulation drilling tools. It is widely used in geological hazard control projects. During the drilling process， the drill bit is subjected to alternating impact load， which is prone to stress concentration and fatigue failure. The stress waves generated by the piston collision with the bit propagate to the contact surface of the bit and rock， and cause the superposition of stress waves， which increases the stress on the bit. In order to ensure the normal operation of the drill bit， the strength analysis of FGQ-600 large-diameter DTH hammer drill bit under impact load is carried out by the Finite Element Software. The results show that the von-mise stress increases with impact energy. The maximum equivalent stress on the bit is 808.9MPa at the impact energy of 2500J of the DTH hammer， which is less than the material yield strength and meets the strength requirements. When tripping， the stress on the pin decreases with the increase of its diameter. The maximum stress on the 40mm pin is 383.66MPa， which is less than the material yield strength of 785MPa and meets the strength requirements.The pin appears plastic deformation at the diameter of 16mm； thus， it is recommended that the diameter of the suspension pin should not be less than 20mm.