The invention relates to the technical field of vehicle square cabin expansion, in particular to a link mechanism for square cabin expansion and an expansion square cabin provided with the link mechanism. When the link mechanism is expanded, two-level expansion can be realized simultaneously; in the expanding process, under the action of driving force, acting force exists between a driving rod and a secondary connecting rod through a fulcrum bar to support the secondary connecting rod. Through reasonable arrangement of all hinge points, component force, which is gradually increased in the expanding direction, of cabin plate gravity can be offset in the expanding process, and therefore smooth expansion of the square cabin is guaranteed. The link mechanism is applied to the expansion square cabin for expansion, top plates and bottom plates at all levels are of foldable cabin plate structures, two-level expansion of the square cabin can be easily realized, and meanwhile the expansion area and space are large.