To investigate the effect of dietary fiber composite on sarcopenia, intestinal flora and derived metabolites like shortchain fatty acids (SCFAs) in aging mice with type 2 diabetes mellitus (T2DM), an aging T2DM mouse model was established by feeding the C57BL/6J mice a high-fat diet along with intraperitoneal injection of streptozotocin and D-galactose. The mice were subsequently intervened with a high-fat diet containing a dietary fiber composite. After 8 weeks, the pathological changes in the skeletal muscle of the mice in each group were found, and their blood glucose levels, skeletal muscle mass, intestinal flora composition, and SCFAs content were measured. The results showed that the insulin resistance index in the aging mice with T2DM decreased significantly upon receiving the dietary fiber composite. The muscle mass and exercise capacity were enhanced by the dietary fiber composite, with the relative weights of the gastrocnemius and tibialis anterior muscles being increased by 23.23% and 22.22%, respectively. The dietary fiber composite reshaped the composition of intestinal flora, and changed significantly the levels of SCFAs in the colon i.e. increased by 175.00% (acetic acid), 59.46% (butyric acid), and 60.87% (valeric acid). Therefore, the dietary fiber composite could effectively ameliorate insulin resistance and sarcopeniain aging mice with T2DM. The potential mechanism might involve modulation of intestinal flora composition to enhance SCFAs production. The results of this study provide a theoretical basis for the application of dietary fiber as an adjuvant therapy in T2DM treatment for the elderly patients.