According to the data collection，8 quantitative factors，such as seepage flow and seepage slope gradient，are selected as the indexes of seepage risk assessment of earth-rock dam，and the objective weights of each index are obtained by the combination of rough set and improved analytic hierarchy process.Combination weighting-TOPSIS evaluation method is established to evaluate and predict seepage risk of six earth-rock dams and obtain seepage safety risk grade of earth-rock dams.The result is consistent with the field investigation.The results show that the method is accurate and convenient for the risk assessment of earth-rock dam seepage，and can be used to evaluate quickly the seepage stability of earth-rock dam.