A turbomachinery casing structure provides the necessary support to many crucial systems and components in an aeroengine such as the combustion chamber, compressors, and turbines. A competitive casing structure should be stiff and durable while minimizing weight. This work investigates the possibilities and potential of using topology optimization to design a turbomachinery casing structure to achieve certain design requirements. As the casing structure is in a high pressure system that undergoes complex mechanical loading conditions, the level set method is employed in contrast to the common density-based topology optimization methods, which could lead to physically uninterpretable gray elements for a complex loading environment. This paper describes the basic concept of the level set method and demonstrates the benefits in terms of boundary definition, speed, and applicability to engineering problems. Topology optimization with a linear-elastic analysis based on an axisymmetric finite element solver is employed in this study. Both minimum compliance and minimum stress problem formulations are considered, and a series of optimum designs are presented and discussed.