Sustainable development has been popularized and emphasized in many industries. Great attention has been paid to the sustainability performance of the whole supply chain, with evaluating suppliers’ sustainability being particularly critical. However, research on sustainable development in the consulting service industry remains to be discovered, and few academic studies have analyzed the supplier selection indices derived from this industry. This paper conducted a case study in a design institute using the Delphi method to investigate the concept and characteristics of sustainable suppliers. Keywords derived from surveys and literature were collected, sorted, and established into a comprehensive hierarchy index system for sustainability evaluation. Finally, based on the improved failure mode and effects analysis (FMEA) and analytic hierarchy process (AHP), the failure risk of the indices was analyzed with weighted risk factors to obtain the high-risk key evaluation indices, which provided a simplified scheme for enterprises to streamline the evaluation process on sustainable suppliers. The results show the reliability of the improved FMEA model by differentiating the risk value and ranking. Suggestions for sustainable improvement are provided.