<p>Laser directed energy deposition (LDED) technology has great potential for the rapid manufacturing of large and complex metal components, but the severe stress and deformation problems greatly limit its development. In order to achieve low stress and small deformation, this paper investigates the inhibition effect of the synchronous water-cooling-assisted method on the residual stress and deformation and, based on the different distributions of the temperature field in the melt pool scale and the component scale, discusses the mechanism of the evolution of the full-cycle deformation, as well as the inhibition mechanism of the method. The results show that during the deposition process, a high temperature gradient at the melt pool scale generates a concentrated compressive stress zone in front of the melt pool, causing reverse deformation of components at the initial stage of deposition of each layer. Tensile stresses introduced behind the melt pool due to cooling contraction increase with the movement of the melt pool, which ultimately counteract the reverse deformation induced by the front compressive stress resulting in forward deformation. The temperature gradient at the melt pool scale leads to an oscillatory increase in the deformation of the components during the deposition process. During the cooling stage, the macroscopic temperature gradient at the component scale causes monotonic deformation. Synchronous water-cooling assistance reduces the extent of the melt pool and heat-affected zone, effectively eliminating the temperature difference at the component scale during the cooling and the associated monotonic deformation. With synchronous water-cooling assistance, the maximum residual stress of substrate decreases by 119.94&#xa0;MPa, and the maximum deformation is reduced by 8.70%. This work presents an effective stress and deformation suppression strategy for LDED, elucidates its mechanism, and offers insights for future studies on deformation mitigation.</p>