Streamlined structure is a special structure which supporting freeform-surface skin. Taking the case of the head structure of a streamlined high-speed train, the characteristics of the streamlined structure were analyzed. Based on this, feature description for streamlined structure was proposed. With the help of the feature, the solid model of the streamlined structure can be easily generated, modified automatically adapted to the change of the streamlined freeform surface. The feature will be beneficial to the finite element analysis of the streamlined structure, comparison among different design plans, for the optimization design of streamlined structure and advanced software development for generation of streamlined structure with the concept of concurrent engineering.