Abstract: This research aims to provide theoretical proof for the further study on the mechanism of stress relaxation during drying under high temperatures and pressurized steam.In this study,Japanese sugi(Cryptomeria japonica D.Don) was used as the experimental materials.Tensile stress relaxation during drying under high temperatures and pressurized steam was discussed using a specially developed load cell,which was capable of measuring stress under high temperature and pressurized steam inside an autoclave.The results showed that the effect of temperature on stress relaxation was much more significant than that of strain level.Stress relaxation dramatically increased and the remaining stress rapidly decreased with temperature enhancing.Stress relaxation was not only affected by the temperature,but also greatly affected by the environmental relative humidity.It was also found that,irrespective of radial or tangential direction,the remaining stress during tensile stress relaxation as well as the maximum shrinkage stress during drying had a good relationship with temperature.The results clarified that the significant reduction of shrinkage stress during drying under high temperature and pressure superheated steam was attributed to the relaxation of shrinkage stress caused by shrinkage deformation due to long-time tensile status.