Abstract In any group decision making, stakeholders have different powers, proficiency and also experiences. These power weights are very difficult to obtain, because group managers avoid revealing the relative powers of the stakeholders to prevent more conflict among them. Therefore, in many studies, the different powers have not been well accounted and then equal power weights have been assigned to each stakeholder. This paper will show that considering the powers is necessary and then it introduces a new intelligent approach to obtain consensus based relative power weights. This method is based on the opinions of the stakeholders on the alternatives. A case study of watershed management is used to illustrate the application of the model to a real decision making problem. A suitable aggregation operator is also used to combine the goodness measures, considering the optimism/pessimism view of the group manager. Results indicate that obtaining the stakeholders’ weights and also considering the preferences of the group manager on the risk are essential parts for soft group decision making process, especially in the environmental management problems.