Abstract ： Resarch purposs ： The railway tunnel portal section is induced by long term thermal - humidity stress in high temperature and high humidity in the south China， surrounding rock and lining structure s physical - mechanical properties will be degraded or weaken by thermal - humidity stress and to influence safety and life of tunnel structure. Based on the theory and model analysis，combined witli field test research，this paper got tlie disease thermal - humidity mechanism of tunnel portal section，to provide the theory basis for disease treatment for tlie portal section of tunnel under high temperature and high humidity environment. This study is lack at present. Research conclusions ：( 1) Based on incremental theoryand humidity - stress theorr，incremental constitutive equations of rock elasticity - plastic deformation produced by high temperature and high humidity were built， and thermal - humidity stress equations were deduced. (2) Based on a certain tunnel field monitorng data， the temperature field， humidity field of surrounding rock and thermal - humidity stress and seasonal changes were analyzed，the influence of different thickness and thermal conductivity coefficient of rock and lining on thermal - humidity stress was studied. (3 ) The radial infuence depth of thermal - humidity stress in rock is more than 3 meters，the distribution and develop ruleof thermal - humidity stress and cumulative effects were fund. (4) This research result will provide the basis for structure design and disease treatment of tunnel entrance in high temperature and high humidity areas.