A multi-stage situation group decision-making model is studied. Based on the quality analysis on decision experts’ evaluation information, the qualitative change and quantitative change of evaluation stages are defined. Then a time weight model minimizing the information deviation for adjacent stages is built, and the value range of Orness measure with the unchanged optimal situation is analyzed, which provides a reference for decision experts to assign the value. A new method for information aggregation is proposed for multi-stage grey situation group decision-making. Finally, a specific example illustrates the effectiveness and feasibility of the proposed method.