Abstract: The whole process of experiment onφ339.7 mm×12.19 mm P110 BC casing running down in well was investigated, and the problems found in the experiment were solved on time for the casing string to run down successfully. The experiment results showed that thread gluing and cross threading happened easily by abnormal stab without using stabbing protector or guiding screw at high speed with power tong instead using strap wrench. It was difficult to guarantee the quality of make up without using stabbing protector and strap wrench. The improper griping position of clamp caused coupling deformation of casing, and led to increase the make up torque. So the make up torque with and without clamp should be decided respectively. In order to guarantee the running down quality of casing, the specification on use and maintenance for casing should be carried out, and the operation procedure on thread protection, cleaning, inspection, repair, thread compounds, stab, guiding screw, the speed and torque and control method of make up should be checked strictly.