The cultivation of design professional degree postgraduates emphasizes practical ability and innovative spirit. However, the current evaluation system generally suffers from overemphasis on academic achievements at the expense of practical ability, disconnection between curriculum and industry needs, and diversity without integration of supervisor teams. Taking the cultivation of design professional degree postgraduates at Hangzhou City University as a case study, this research constructs a multi-dimensional evaluation mechanism centered on practical outcomes from three dimensions: evaluation orientation transformation, teaching model reform, and supervisor collaboration optimization. By building interdisciplinary supervisor groups, implementing real-project-driven practical teaching, establishing a multi-stakeholder evaluation system, and using information technology for process data collection and dynamic feedback, this study explores a feasible path for transforming the evaluation system for design postgraduates. In a two-year action research project, a controlled experiment was conducted on 14 postgraduates (7 in the reform group, 7 in the control group). Data were collected through questionnaires, in-depth interviews, and outcome comparisons. The results show that the reform group significantly outperformed the control group in design intention clarity, practical problem awareness, supervisor feedback benefit, and evaluation fairness. The participation rate and award rate in design competitions, as well as the average blind review score of teachers, were significantly higher. This paper provides operational experience and reference for the evaluation reform of postgraduate education in design and related disciplines.