In the big data era, designers face huge difficulty in collecting numerous cases of site design on the Internet. To enhance retrieval efficiency of designers, the present study develops a method based on extension set to retrieve site design cases and approaches to formulate innovative strategies. First, data acquisition software is adopted to acquire site design case data, and the data server, database development and programming software are comprehensively and jointly employed to build a case base of site design. Second, based on the retrieval condition converted from site design contradiction, site design cases are initially screened out by correlation function, and then they achieve dynamic optimization sorting based on extension set theory, as an attempt to satisfy personalized needs of designers. Lastly, innovative strategies for site design are automatically formulated on case base. As suggested from case test, this method is capable of helping designers efficiently retrieve valuable cases of site design on the Internet, thereby presenting some theories and methods for intelligent site design.