According to the principle of unsaturated seepage and taking the clay core wall earth-rock dam in Sifangjing Water Conservancy Project as the research object, the seepage characteristics and anti-earthquake stability of the upstream and downstream dam slopes of the clay core earth-rock dam under the accidental earthquake of sudden drop of reservoir water level was simulated and analyzed. The calculation results showed that the greater the rate of water level drops, the more severe the pressure of the upstream dam slope is, the smaller the coefficient of safety stability is. The higher the location of the monitoring point is, the more difficult it is to reach the stable value of the pore pressure. For the downstream dam slope, the change of pore pressure is relatively gradual, the farther away from the groundwater level, the more difficult it is to stabilize the pore pressure, and the longer the response time of pore pressure to respond to the sudden drop of reservoir water level. When the reservoir water level drops suddenly to the dead water level, the larger the sudden drop rate, the smaller the safety factor, and the larger the Newmark displacement. The safety factor of downstream dam slope is not sensitive to the plummeting rate, and the safety factor is basically the same, and Newmark displacement is very close. The research results can provide some reference for the actual project management and operation.