Under the background of Chinese urban construction from incremental development to stock renewal, architectural education is also actively responding to explore the teaching methods and ideas for urban renewal. In recent years, urban renewal has become a hot discussion topic in design teaching of senior grade, and also a frequent topic of joint graduation design. This paper takes a part of the graduation project of "the Joint Graduation design of four Schools" as the object, analyzes the concept of "visualization city" based on image algorithm proposed in the teaching process, including three levels of urban cognition, urban visualization model construction and renewal strategy, tries to construct the visualization city model of Xicang block through the cognitive image containing material and non-material elements in the urban pixel operation. The strategy of continuing and enriching the regional characteristics of diversified integration of the base from the aspects of culture, business form and residence is put forward. Finally, the positive overlapping design is applied to activate the urban vitality of Xicang block at the specific operation level, and it is proposed that the method of urban cognition which integrates rational analysis and perceptual cognition should be established and enriched to cope with the transformation of digital information age. Architects in the new era, as the first generation of Aborigines in urban renewal, should understand urban constancy from the perspective of reallife. The inner meaning of urban design is to mediate the complexity and contradiction of urban space through the intervention of design. Therefore, it is necessary to revise the traditional teaching concept aiming at training professional architects, from the training of design-only skills and special abilities to cross-disciplinary comprehensive quality training, so as to re-understand the professional orientation of architects under the demand of urban development in the new era. This is of great significance to the sustainable development of architecture discipline.