Abstract: The authors studied the residual stresses of axi-symmetrically deform-strengthened retaining rings　as outcomes of restrained spring-back after deformation. The complex problem in mechanics is　simplified by dissolving the 3-dimensional systems of strains and stresses into two 2-dimensional　systems. The mechanism of formation of residual stresses and their relationship with deformation　methods were studied.　For explosion-deformed retaining rings, the authors put forward the principles of "outside inflexion" and "Single explosion-uniform deformation", which will ensure low residual stress. A new and more relevant method of measuring residual stress as a function of radius r and height x is worked out. Several explosion-deformed, mechanically deformed (with spheroidal expansion-dies) and hydraulically expanded retaining rings were cutup and residual stresses measured by the new method. Results of actual measurements agree with theoretical analysis. From these results, the authors established the theoretical basis of lowering the harmful residual stresses of retaining rings by superposing of stresses, and designed new hydraulic devices for this purpose. The new devices are also used directly for producing hydraulically expanded retaining rings with low residual stresses. After successful test productions, this new technology in now in production use.