Abstract: The base of an isolated structure always has special load bearing properties during its construction period, because the restriction provided by the isolation layer to the superstructure is weak when compared to a fixed base of a structure. For a long complicated isolated reinforced concrete structure, a large lateral displacement occurs in the rubber bearings, which has been proved to be caused by some non-loading factors such as temperature variation, and the shrinkage of concrete. When the construction scheme is poorly worked out, there might be some cracking in the RC girders of an isolation layer. This paper presents mechanics of a long isolated time varying structure under its construction process with an irregular plan. The discrete time freezing method, i.e., the structure is physically regarded as a time-invariant structure with varying topology at a specified time step. Numerical result shows that the construction scheme is more suitable for the construction of an isolated structure, the cracking in the RC girders of the isolation layer is caused by construction loading, intensive temperature fluctuation, the shrinkage of concrete, and the early removal of mould. The bearing displacement, deformation and internal forces of floors caused by non-load deformations are analyzed in a construction process.A reasonable layout for a latter pouring belt is presented by the displacements of rubber bearings and beams. The correlation between the non-loaded displacement of rubber bearings and the environmental loading is verified through a monitoring system installed on an isolated structure during its whole construction process.