Abstract: Obvious process induced distortions usually take place in complex wing structures made of polymer-matrix composites. This leads to problems in the assembly and aerodynamics performance of composite wings. The objective of the present work is to develop a hot sizing process for large and complex composite structures, to solve the distortion control problem of composite wings. New sizing tools were designed according to the process induced distortions of wings, to carry out hot sizing experiments. A finite element simulation method was built up to predict the final shape of wings after hot sizing, based on characterizing the stress relaxation property of composites. The effects of process parameters were analyzed including temperature, sizing loads, et al, in order to optimize the hot sizing scheme. The simulation and experiments results show that hot sizing process is valid for large and complex composite structures. 89.5% of the process induced distortions of the composite wing structures is compensated by the hot sizing process, meeting the geometry requirements for assembly and aerodynamic characteristics.