In this paper,  an environmentally friendly hydraulic percussive drill is introduced,  in which water is used to perform all function of the drill,  such as energy transmission,  push,  chip removing and lubrication.  Then,  dynamics of the percussive drill is modeled by means of elastic bars and springs,  and microcomputer simulation of YST-25 environmentally friendly water hydraulic percussive drill is performed.  The performances of YST-25 environmentally friendly water hydraulic percussive drill are evaluated.  The result indicates that piston meets intensity design demand,  maximum compressive stress of which is 102MPa and maximum tensile stress is 28MPa.  The stress of drill rod is bigger than that of piston.  To reduce the variation of sectional area is helpful to elongate the life of piston.  YST-25 drill is more suitable to drill medium or hard rock so as to keep synthetically both drill speed and energy transfer efficiency.  The suggestions can improve the design of environmentally friendly hydraulic percussive drill.