Abstract: Initial geostress has a direct influence on wellbore stability and casing integrity. Consequently, it has a significant influence on the efficient production of a well. Aiming on the optimization of a wellbore trajectory in terms of easy drilling and casing integrity, the concept of Formation Loading Potential is proposed here for the mathematical representation of geostress characteristics of a formation. The lower the value of Formation Loading Potential is, the more favorable the trajectory is to the drilling and casing integrity. Furthermore, the numerical estimation of casing integrity needed at some crucial well sections can be determined with reference to the distribution of the Formation Loading Potential. Results of numerical validation indicate that the concept of Formation Loading Potential is reasonable, and the procedure of numerical calculation is efficiency and practical. This study provides the industry an easy and practical tool for trajectory optimization.