Thermal performances of an advanced mechanically joined module (MJM) under steady state high heat fluxes of 2.0-4.25 MW/m(2) and thermo-mechanical analysis are described. The advanced MJM was designed to apply for a helical divertor plate of a large helical device (LHD) at the next experimental phase II. The advanced MJM has a unified armor/heat sink made of carbon/carbon composite different from the normal MJM with a separated copper heat sink. To evaluate the thermal performance of the advanced MJM, short pulse high heat flux test up to 5.4 MW/m(2) and steady state high heat flux tests up to 4.25 MW/m(2) have been carried out using a test facility ACT. Moreover. the thermal fatigue test of the advanced MJM up to 150 cycles under steady state high heat flux of 2.5 MW/m(2) has been performed. After theses tests, no apparent damage and no cracking on the armor tile were observed although there was a little increase in the armor/heat sink temperature during the thermal fatigue test. To evaluate the thermal stress in the armor/heat sink of the MJM during steady state high heat flux test and to optimize the structure, thermo-mechanical analyses are done using a 3D CAD. (C) 2001 Elsevier Science B.V. AR rights reserved.