In sports facilities, a grandstand is the structure which provides good sight quality and safety evacuation conditions for the spectators. Grandstand plays important functional and formative roles in sports facilities, and especially in large scale stadia. This paper argues the notion of shape grammar and its computer implementation will solve the difficulties in grandstand design. The authors identify the specific difficulties of grandstand design, then set the aims of the grammatical computer tool. Afterwards the shape grammar of grandstand design is formulated, and a computer tool is developed based on the grammar. At last, the paper discusses the application and usage of the grammar and the computer tool both in early design phase and design development phase with a design practice case study of a large scale stadium.