Beginning with such factors as social cultural background, social economic background, ecological and social psychological background which influence tourism bearing capacity, the article puts out the tourism bearing capacity index and its arithmetic model of operation and gives out a case of its application. The authors define the tourism environmental bearing capacity as the bearing intensity of tourism destination during a period which doesn’t do harm to the present and future people in its current state and which can be accepted by the residents. The bearing intensity of tourism destination mainly includes three sub class indexes: the tourist density, the tourism land use intensity and the tourism income value. To calculate the tourism Activity Intensity in a comprehensive indicator, the Tourism Bearing Capacity index is defined by the authors as a non—dimension value which can be an assessment indicator for sustainable tourism.