Abstract: In view of the situation of the heavy metal pollution of tailings reservoir seriously harm the ecological environment and human life,taking 6 different tailings reservoirs in Liaoning Province as research objects，the method of grey target decision is used to make the quantitative research and evaluation on their pollution. Pollution of different heavy metals to the environment is systematically analyzed and 7 heavy metals including Zn，Pb，Cd，As，Cu，Cr，Hg were selected as indexes to set up the heavy metal pollution of tailings reservoir evaluation system. The analytic hierarchy process(AHP) and entropy weight method are adopted to determine the subjective and objective weight，the final combinational weight of evaluation index impacting on the tailings reservoir pollution is obtained by the combined weighting model. Based on the grey system theory，multi-index heavy metal pollution of tailings reservoir grey target decision model is built. The pollution critical concentration is determined as the optimal effect vector，that is，the target of the grey target decision-making model. The off-target distances of six undetermined blocks between effect vector and the optimal effect vector are calculated out. According to the value of off-target distances，the pollution of six tailings reservoirs can be ranked. The bigger the off-target distance is，the more serious the mine pollution is. The evaluation result is in good agreement with the actual situation，which indicate that the grey target decision model of multi-index heavy metal pollution of tailings reservoir based on combinational weight for evaluating pollution of tailings reservoir is feasible.

Key words: Tailings reservoir, Pollution, Combinational weight, Evaluation, Off-target distance