Abstract: Different water content states have important influence on the mechanical property and failure mechanism of rock. In order to study the mechanical property and energy mechanism of mudstone with different moisture contents,the conventional triaxial compression tests under different confining pressures on dried,natural and waterlogged samples are conducted using RMT-301 rock mechanics test system. The results show that with the decrease of moisture con- tents,the total energy absorbed by mudstone increases. In compaction and elastic stage,the elastic energy decreases with the moisture content increases. In the elastic-plastic stage,the growth rate of elastic energy decreases,and in the stage of instability and failure,the lower the water content,the higher the elastic storage energy. The limit of storage energy decreases linearly with increasing moisture content under the same confining pressure. In compaction and elas- tic stage,the dissipated energy grows slowly and increases as the moisture content increases. In the elastic-plastic stage,the proportion of dissipated energy to total energy grows rapidly. The growth rate of dissipated energy increases as the moisture content decreases. The results of acoustic emission show that the higher the moisture content and confining pressure,the lower the rate of acoustic emission events and the less the internal orientation events of rock,which indicates that rock internal failures are more intensive with lower moisture contents and smaller confining pressure.