To facilitate the design and construction of complex functional materials, the field of molecular assembly can learn from the well-established field of catalysis including its branches such as electrocatalysis and photo-electrocatalysis. In this study, we establish a "photo-electro-catassembly" strategy to repeatedly fabricate two-dimensional molecular assemblies on electrode surface by learning from the concept of photo-electrocatalysis. With the rational design of the linear diacetylene building blocks, Au electrode surface itself and the thiol-functionalized electrode both can assist the formation of two-dimensional assemblies and their subsequent covalent stabilization through the polymerization of diacetylene groups. Nevertheless, when using the Au electrode surface as a direct template, the polymerized product would be hardly removed from the electrode due to the strong synergistical interactions through multivalent Au-S bonds. By contrast, when using the thiol-functionalized electrode as an indirect template, the diacetylene building block forms a well-ordered second layer over the thiol monolayer due to the solvent-phobic and solvent-philic effects. After photo-polymerization, the polymerized product can still be removed from the electrode along the electro-induced removal of the thiol monolayer. Driven by electricity and photoirradiation, the thiol-functionalized electrode assists the combined process of assembly and photo-polymerization as a "photo-electrocatassembler", and it works repeatedly to produce covalently stabilized two-dimensional assemblies. (C) 2017 Published by Elsevier Ltd.