Abstract: Casing worn out, especially worn-out at well head is a common problem in all of the oilfields. The casing damage at well head is related to the wellhead eccentricity, hanging load, casing head structure, drilling technical parameters, casing materials and so on. This paper gives an investigation on casing worn out at the well head of some oilfield, and analyzes mainly the effect of well head hanging load and casing head structure on casing worn out at well head. The optimization calculation formula for decreasing the whole casing hanging load effectively is given by calculating and researching well hanging load. The formula is applied to calculate casing hanging load in actual well cementing, and the results show that the calculated hanging load is benefit to prevent casing failure at well head from. Finite element analysis software ANSYS has been used to study the influence of slip force on casing, and it found that the stress concentration located at casing inner surface position where the two ends of slips, and optimization of designed slips is suggested.