Abstract：Casing damage is the bottleneck problem for oil and gas production. Reasonable design of collapse load is vital to the life of casing. Former researchers considered the formation to be orthotropic and transverse isotropic. But the rock mechanics orthotropy in the plane perpendicular to well axis is not taken into account. Based on this point，the mechanics and finite element models for casing stress calculation are established. The results show that casing stress presents uniform distribution situation if the formation is transverse isotropic with the uniform horizontal in-situ stress. If the formation is orthotropic，however，the casing stress becomes non-uniform distribution. At the same time，the maximum casing stress is larger than the former. So it is obvious that the formation orthotropy has great effect on the casing stress，which should be considered in casing design process. This conclusion is also helpful for explaining the question that casing collapse load maybe larger than the overburden stress some times. When the horizontal in-situ stress is non-uniform，the casing stress is non-uniform at all times not only in the isotropic formation but also the orthotropic ones. At the same time，the maximum casing stress is almost same to each other. Therefore，under this condition，the rock mechanics orthotropy problems can be overlooked during the casing design process.
