Abstract: In view of the problem of thread gluing of casing thread in a gas well, the macro observation, thread parameter measurement and scanning electron microscope analysis were used to analyze its causes. The screw on and screw off test was carried out on the same type of new casing. The results show that the thread parameters of the casing met the requirements. The uneven thickness distribution of casing thread phosphating layer and poor anti-sticking performance of casing were the main reasons for the thread gluing of casing thread.