Abstract: A U-shaped thin-walled structure part model of T300 carbon fiber reinforced AG80 epoxy resin (T300/AG80) composite was established by ABAQUS finite element software. The stress and springback amount (synchronous demolding by simulation) changes during hot-press curing molding and the residual stress distribution after demolding were studied. The simulation of residual stress was verified by the small-hole test method. The results show that during the molding process, the stress and springback amount of the side wall and bottom surface of the U-shaped structure part increased with time. The stress and springback amount increased with the distance from the bottom surface or the distance from the center of symmetry. After demolding, the residual stress at the center of symmetry of the U-shaped structure part was the smallest, and the residual stress increased with the distance from the bottom surface or the distance from the center of symmetry. The greater the residual stress released before and after demolding, the greater the springback amount. The relative error between the residual stress measured by the small-hole method and the simulation was less than 10%, indicating the simulation was accurate.