Bonded piston seals (BPSs) which consist of metal ring and rubber lips are used as hydraulic pistons for Automatic Transmission (AT) or Continuously Variable Transmission (CVT). While engaging clutches, BPSs preserve the hydraulic pressure, therefore it is necessary to endure number of cyclic pressure through the life. This paper describes a reliable design method of BPSs with taking account of the influence of residual stress on the fatigue limit of the metal ring. A new plastic-elastic analysis model considering Bauschinger effect is applied in order to estimate the residual stress, which generates due to metal forming process. Validation for calculated residual stress is done by X-ray diffract meter. A proofed BPS design calculated with this new FEM model shows longer fatigue life than conventional design.