The quality of hydro-expanded double-layered tubes depends on the hydro-expanding pressure. Therefore, it is very important to determine the range of the hydro-expanding pressure accurately during the fabrication of double-layer tubes. According to theories of elasticity and plasticity, the responses of double-layered tubes subjected to five kinds of cases were analyzed during the hydro-expanding process. And the stress and strain for inner and outer tubes of double-layered tubes were discussed. By using the relation of deformed compatibility of hoop strain, suitable condition of hydraulic expansion and variable range of hydro-expanding pressure were obtained, and the calculating formulas between the hydro-expanding pressure and residual contact pressure was derived. Use the non-linear FEA MSC.patran/marc code to simulate the deformation and stress distribution, the whole process of hydraulic expansion was numerically investigated, in which the nonlinearities of the material, geometry and contact were all taken into account. The results show that the range of the hydro-expanding pressure from the numerical simulation is in good agreement with those from theoretical calculation with a maximum relative error of 6.52%. The investigation on the hydraulic expansion of double-layered tubes may guide the engineering design and provide references for further research.

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