Abstract: In the presplitting blasting excavation of dam foundation gentle slope, to solve the problem of low drilling efficiency when the production blast-holes or buffering blast-holes are traditionally arranged along the slope (blast-holes along the slope, BHAS), the engineers try to adopt the way of reverse slope drilling (blast-holes reverse the slope, BHRS). However, the dynamic responses of rock mass under different ways of blast-hole arrangements are different. So, it is necessary to compare the disturbance of the reserved rock mass in dam foundation under the two aforementioned ways of blasthole arrangements. Based on the gentle slope excavation of the dam foundation of Baihetan Hydropower Station, onsite blasting experiments were carried out under the two ways of blasthole arrangements, namely BHAS and BHRS. At the same time, the blast-induced damage evolution characteristics and vibration distribution law were analyzed under the above two ways of blasthole arrangements, by using the 3D dynamic finite element numerical simulation software (LS-DYNA). Moreover, the inherent mechanical mechanism under different ways of blasthole arrangements was revealed. Finally, the choice of the excavation scheme for the gentle slope of dam foundation was discussed from the views of the forming effect and construction efficiency. The results indicate that the disturbance of the reserved rock mass induced by presplitting blast-holes is basically the same under different ways of blast-hole arrangements. Nevertheless, the cumulative damage effect and blast vibration caused by production blastholes and buffering blastholes are different. The inherent cause lies in the change of the intersection angle between the blast-hole and the reserved rock mass surface. Compared with the BHAS, the explosion energy transmitted to the reserved rock mass was reduced, as the BHRS increase the intersection angle between the production blastholes or buffering blastholes with the contour surface. Thus, the BHRS is beneficial to reduce the disturbance to the reserved rock mass, which can reduce the damage depth by 11.6%~13.9% and the vibration velocity by 6.4%~53.7%.