Abstract: Underground rock engineering is mostly in different water environments. Water content has become an important factor affecting the dynamic mechanical response characteristics of engineering rock mass, which seriously threatens its safety and stability. The red sandstone was used to prepare specimens with four water content, and the SHPB test system was used to conduct the impact test with the same impact velocity. On the premise of analyzing the relationship between the Young's modulus of red sandstone and water content, the total input strain energy, releasable elastic strain energy and dissipated energy of red sandstone with different water content were calculated, respectively by energy calculation. The evolution of three kinds of energy with time and strain were studied to judge the initial time of growth of microcracks and failure of rocks, and analyze the damage characteristics. The results showed that the Young's modulus, crack initiation time and failure time of red sandstone decreased first and then leveled off with the increase of water content. With the increase of water content, the initial strain of each energy evolution stage first increased and then decreased, and the ratio of dissipation energy to total strain energy increased first and then decreased at the beginning of the failure(unloading) stage. The damage accumulation rate of red sandstone increased in time scale and strain scale with the increase of water content.