Sustainable supplier selection is the essential core of sustainable supply chain management, which can directly influence the manufacturer’s performance and can enormously enhance the manufacturer’s competitiveness in the international market. However, most of the previous studies concerning sustainable supplier selection have less focused on the reliability of the decision-makers judgments and the application of regret theory. To fill this gap, we presented an integrated sustainable supplier selection model based on regret theory and QUALItative FLEXible multiple criteria method (QUALIFLEX) under a 2-dimensional uncertain linguistic variable (2-DULV) environment. In the proposed model, 2-DULV including the reliability of evaluation information is employed to handle the uncertainty and vagueness of decision-makers judgments. A similarity-based method is used to derive the decision-makers’ weight, and a maximizing deviation model is established to calculate the weights of evaluation criteria. Then an improved QUALIFLEX method based on regret theory is presented to obtain the ranking order of sustainable suppliers. The proposed approach integrates both the superiority of 2-DULV in effectively handling the uncertainty, vagueness, and reliability of evaluation information and the merit of regret theory in dealing with decision-maker’s bounded rationality. Finally, a numerical example concerning an automobile manufacturer is provided to validate the effectiveness and feasibility of the presented model.