Abstract: Sketch-based graphics input is a natural and effective way to present designer's intention and transfer conceptual idea into ideographic representation. A prototype of sketch-based graphics input tool is realized for scheme design, which is based upon on-line graphic recognition and similarity-based relevance feedback. Online graphic recognition can reveal latent primitive shapes from user-drawn strokes and show the regularized shape on screen immediately through geometric preprocessing, feature recognition, shape fitting and regularization. After the primitive shapes are grouped according to the spatial and temporal relationships, similarity-based relevance feedback are introduced to catch and suggest the user intention through computing their similarity with the predefined template both in partial structures as well as in overall configuration. Experimental results show that this tool can yield good results of precise recognition and fine response to user interaction. The proposed idea presents a novel way for computer supported schematic design.