The invention discloses a construction method for a movable observation and construction dual-purpose platform. The method includes the steps that a field is leveled, a side slope soil body is cleaned and leveled, loosened stones and protruding lone stones are eliminated, two rows of idler wheel sliding grooves are formed in a pit bottom and the top of a side slope according to the intervals of idler wheels, the two sides and the bottom of each idler wheel sliding groove are leveled and compacted, and it is guaranteed that the movable platform slides in the idler wheel sliding grooves without obstacles; a scaffold is erected at the pit bottom; a body of the scaffold is erected between the pit bottom and the top of the slope; and the scaffold is moved for acceptance inspection. By the adoption of the method, a pipe gallery can be dynamically observed in the walking process, the circulation pressure applied by a project to the scaffold is relieved, the construction efficiency of an outer wall is improved, and the schedule of the whole project is accelerated; and the technical problems that a traditional fixed scaffold platform is long in erection period, inconvenient to use and large in detaching work amount are solved, and a creative solution is provided for erection of the pipe gallery construction platform.