The representative cases of underground engineering constructed by shield or pipe jacking with span more than 10 m and large rectangular crosssections are studied. And then the mechanized construction technologies for underground engineering with large rectangular crosssection are divided into 4 types, i.e. fullsection construction technology of rectangular tunnel, bench excavation technology for largesection tunnel, construction technology for multitunnel and structural cat and convert method; the basic concepts, typical cases, applicable scopes and technical characteristics of the technologies are introduced; and the principle, technical characteristics, application points and engineering project of structural cut and convert method are introduced emphatically. Finally, based on the engineering background and the basic principles of engineering research, an innovative research idea of mechanized construction technology for largescale rectangular crosssection underground engineering is put forward, which takes the feasibility as basis, quality, safety and environmental protection as foundations and efficiency improvement and cost reduction as goals.