In order to explore the dynamic strength and failure mechanism of red sandstone under condition of hydrochemical damage, the static uniaxial compression and dynamic uniaxial impact tests of natural, dry and water saturated red sandstone samples are carried out. Combined with the SEM images of rock fragments, the strength characteristics of rocks under condition of different water bearing and strain rate loading levels are analysed, and based on the damage fracture theory, the initiation and propagation mechanism of micro cracks in water bearing rock are analysed as well. The test results show that the dynamic compressive strength of red sandstone decreases with the increase of water content and increases with the increase of strain rate, and the saturated sample has significant strain rate effect; under condition of impact load, the stressstrain curve of saturated sample has significant volume compression phenomenon, with the maximum peak strain and obvious plastic deformation, while the dry sample has the largest elastic deformation and the smallest plastic deformation before the peak; under the influence of pore water, the grain structure of saturated sample is loose and porous, and the cementation is weakened by dissolution of cementation material. According to the theory of maximum circumferential normal stress, the conditions of initiation and propagation direction of micro cracks in water bearing rock are discussed, and a modification to the dynamic stress intensity factor at crack tip is made.