This paper presents a novel computational approach that uses tree based genarative algorithm to generate design. This approach is illustrated by a reading lamp design example, which uses general mathematical expressions and tree-based genetic algorithm to generate 2D sketch shapes. Then, these 2D sketch shapes are processed to form 3D components and saved in component base. A complex design is produced by combining different components. The result shows that approach is able to generate some innovative solutions and demonstrates the power of computational approach.