Inbetween the many factors, which will influence the distribution character of initial stress in a mountain, different angle of mountain slopes and horizontal geostress will have important effects on it. Therefore, stress distribution in mountains under different slope angles with considering different lateral coefficients of initial stress is studied using numerical method in here. In this paper, the initial geostress distribution of mountain at typical vertical profiles are studied in the gravity field, with the slope angles being 30°, 45° and 60°, respectively. After the calculation, it can be known that the actual initial vertical stresses may be 2-5 times of the gravitational stresses calculated by direct depth gh for some zones. Meanwhile, it reveals that different horizontal geostress has a momentous impact on it as well. Computation of damage-fracture model for jointed rock is adopted to analyze the rock stability of a cavern. Comparison of the rock stability excavated in a mountain area or under a flat surface is made also.