Abstract: Tripping and galling reasons for φ177.8 mm×10.36 mm 110 premium connection casings in a well were analyzed. It was considered that the tripping and galling of the premium connection casings were related to abnormal operation during running down casing. The pin thread, torque shoulder, and metal to metal seal area of the casing connection without thread protector were easily damaged during running down casing. Incline stab could take place as the stabbing protector was not used during stabbing for make up. Making up at high speed without leading to engagement could result in galling and wrong thread engagement. Once galling and wrong thread engagement appeared, the tension strength of casing connection would be reduced greatly, and tripping accident could occur as the casing string was lifted up.