This research aims to study the dynamic trend of city brand image in the background of convergence media, and to explore the concept and characteristics of dynamic city brand image. The research analyzes the expression of dynamic logo repetition, rotation and gradient in the graphics; the design of dynamic auxiliary graphics applies complete logo shape, logo combination, interception of some elements of the logo and multiple auxiliary graphics; dynamic information graphics are expressed in the form of time progress framework, spatial framework and logical framework; dynamic brand color is a dynamic transformation based on traditional color matching and the dynamic brand color is a dynamic transformation of the traditional color scheme in terms of hue, brightness and saturation contrast. Furthermore, the specific performance of dynamic city brand image is analyzed from the perspective of sound and space. In the context of "convergence" media era, dynamic city brand image design reflects the recognition, diversity and interactivity of dynamic city brand image. In addition, as a form of expression that can efficiently convey the spirit of city culture, dynamic city brand image not only allows audiences to perceive and experience from multiple dimensions, but also allows them to exchange information in a relaxed and pleasant state.