Rainfall and seismic activity have significant influence on the stability of dangerous rockmass. In this paper, the dangerous rockmasses are classified into three instability types according to the failure modes: sliding, falling, and toppling. The discrete element method (COMSOL) was carried out to investigate the stability of three different rockmass types. In the numerical simulation, three load combinations were applied to the numerical model: 1) rockmass weight, 2) rockmass weight + fissure water pressure, and 3) rockmass weight + fissure water pressure + earthquake force. The results show that rainfall and seismic activity play important roles in rockmass stability and the displacement and principal stress of the rockmass are influenced obviously. Wangxia dangerous rockmass in the Great Three Gorges area was selected as a case study, and its stability was analyzed by geological investigation, numerical simulation, and static calculation methods. The results show that there is a high risk that Wangxia dangerous rockmass would lose stability when rainfall season comes and seismic activity happens. A blast was conducted to remove this dangerous rockmass and an SNS net design was proposed to intercept distributed blocks based on rockfall trajectory simulation. The parameters needed in the rockfall simulation program were obtained by laboratory and field tests. Final application proved that the designed treatment is efficient and no damage was caused by the distributed blocks. The whole research may provide a useful reference to similar engineering projects in the future.