To determine the best radius of elastic-plastic interface is the key in the self-reinforced technology. When high pressure vessel was designed and calculated in the use of the self-reinforced theory, the best pressure which was done with self-reinforced and the best radius of elastic-plastic interface were the main parameters. Authors had calculated three different kinds of thick cylinders using ideal plastic material model and damage model. And which compared with the ideal elastic-plastic model and the actually measured radius of elastic-plastic interface with the same parameters. Therefore, the ideal that to determine radius of self-reinforced and elastic-plastic interface which belongs to single and thick cylinder based on damage theory is right. The idea provides a theoretical basis for predicting and controlling residual stress of self-reinforced vessel.