Abstract: The formation of large and complex steel structures, including their geometric configuration and force state, has consistently been a key focus in construction, for large and complex steel structures have always been the key concerns during construction. There is usually a deviation in displacement and force distribution between constructional completed state and structural design state for large and complex steel structures. In order to realize the difference of completed construction and design in structural deformed and force states and ensure structural safety requirements, it is necessary to analyze and control them during construction. Based on the long-span cantilevered trusses of Shenzhen Free Trade Center project, the paper investigated the structural displacements and stress variations during construction by taking into account step-by-step loading and hardening of fluid concrete during pouring, especialy in the calculation and convergence of pre-set deformation values. The safety of the construction process was evaluated and the reasonable construction suggestions were put forward. The results highlighted the significant impact of the concrete hardening process on the pre-set deformation values and stresses, emphasizing that this factor could not be overlooked. The excellent convergence of the forward installation iteration on the pre-set deformation values of the cantilevered truss could ensure the accuracy of the results in the first iteration. The end of the concrete floor slab, if poured directly with the main structure, was constrained rigidly, which results in excessive stress under loads. To solve this problem, pour strips could be used for releasing stress.