Background: The number of patients with diabetes has been increasing rapidly according to a 2017 report by the International Diabetes Federation. Diabetes has become one of the most challenging public health problems, and there will be an estimated 143 million patients with diabetes in China by 2035. This puts considerable pressure on nurses who specialize in the care of patients with diabetes in China and increases related social and financial burdens. Clinical practice has proven that strengthening the core competencies of nurses and establishing an evaluation system of core competencies improve both healthcare quality and patient quality of life. However, no core-competence system framework currently addresses the unique characteristics of nurses in China. Purposes: The purpose of this study was to construct a core-competence system framework for primary nurse specialists in diabetes care. Methods: A brainstorming approach was conducted that worked to conceptualize the core competencies of nurse specialists in diabetes care in China. Next, a study group organized this information and conducted a seminar; 50 experts and patients with diabetes were invited to develop the first draft of the framework. Afterward, 50 experts were selected to participate in the Delphi survey. Most indicators were retained after a three-round Delphi process, and the superiority chart was used to determine the weights of the six dimensions. Results: Forty-seven experts completed the consultation. The experts' rate of response ranged from 94% to 100%, the authority coefficient was .91, and the Kendall's coefficients of concordance in Grades 1–3 were .793, .418, and .542, respectively. An increasingly detailed, three-grade system framework was developed, including six first-grade indicators (diabetes professional knowledge, diabetes-related knowledge, communication skills and health education ability, specialized skills, clinical judgment, and specialty development capacity), 23 second-grade indicators, and 87 third-grade indicators. The weights of the six first-grade indicators were .221, .149, .192, .209, .160, and .069, respectively. Conclusions: The core-competence system framework includes six core competencies, which represent the main characteristics of primary nurse specialists in diabetes care who are highly recommended by experts. It is important to keep in mind that this is only a theoretical framework and thus must be further tested in clinical practice settings in China.