As the characteristics of fragile surface and easy relaxation,it is rare that the columnar jointed basalt is the base rock of the 300 m high arch dam abutment.During the construction of bedrock surface on the columnar jointed basalt rock,some problems often occur,such as destruction of the pre-crack surface of slope,serious pre-excavation of the pre-crack surface,low half-hole ratio of pre-crack surface and rock mass disturbance.In order to solve the stability problem of the broken rock mass excavation and reduce the pre-splitting blast damage to the foundation surface stability,a blasting type was determined by comparison test of the pre-splitting blasting and smooth blasting according to the physical and mechanical characteristics of the columnar jointed basalt on the left bank of Baihetan Hydropower Station.Meanwhile,The parameters of charge line density and hole row spacing of pre-split blasting were optimized.The results show that the comprehensive effect of pre-splitting blasting is better than smooth blasting.The damage of surrounding rock mass was monitored by arranging geophysical monitoring instruments before and after explosion.The blasting parameters of 0.6 m spacing of pre-splitting blasting hole and 240 g/m linear density are obtained,which can minimize the disturbance to the bedrock surface of columnar jointed basalt and achieve the best blasting effect.It provides theoretical and practical reference for foundation excavation of high arch dam with strongly unloaded rock mass.