Abstract: In order to reduce the stress concentration and avoid the breaking of the ring carrier in the piston of a cer-tain medium-speed diesel engine under thermal load‚3D finite element models of the piston and the ring carrier were established‚with which the finite element calculation and analysis of the temperature field‚the thermal deformation and the stress field for the ring carrier were carried out．The temperature field and the thermal deformation were con-sidered as the boundary in the calculation of the stress field‚thus obtaining an integrated stress field of the ring carrier under thermal load．The consistency between the finite element analysis result and the actual result reveals that the two methods of separate analysis and freedom degree coupling on the interface of the piston and the ring carrier are adaptive to the stress analysis of the ring carrier under thermal load‚with the advantages of simpleness and practicality．The an-
alyzed results show that a greater stress concentration would appear in the fixing hole of the ring carrier and that the
structure fault of the fixing hole is one of the main reasons for the ring carrier breaking．

Key words: piston, ring carrier, stress field, finite element analysis, heat transfer coefficient