||Multi-touch technology has been applied to many digital devices. Traditional user interface (UI) is not suitable for these devices since multi-touch technology provides a much different way of interaction. This thesis presents a city modeling application that adopts multi-touch as its input method. The target platform is a device equipped with a large horizontal screen and multi-user interaction support. The application was designed as a game, which allows multiple users to create and edit a model city collaboratively. Its UI consists of two parts: a global navigation system and an editing system for individual users. Each part provides several operations, e.g., view rotation and building creation. We designed a complete set of multi-touch gestures for these operations, as well as some special components for the UI such as a navigation widget and editing windows. The objective is to make the UI intuitive, effective and user friendly so that the users can easily learn to use the application and quickly build a city with it. To achieve this, our designed UI follows several design guidelines: UI orientation-independence, intuitiveness, gesture simplicity and consistency. Finally, we designed some experiments and did a user study to evaluate the UI. The results showed that our UI design was intuitive and comprehensible; and the multi-user support is effective.