Objective: To construct an evaluation index system for nursing quality in patients with diabetes mellitus complicated by coronary heart disease based on the structure-process-outcome three-dimensional quality evaluation model. Methods: Using Donabedian’s three-dimensional quality evaluation model as the theoretical foundation, an initial index system was formed through literature analysis and interviews. The Delphi method was employed to solicit opinions from 24 experts over two rounds of correspondence to screen the indicators. Subsequently, the Analytic Hierarchy Process (AHP) was used to determine the weights of indicators at all levels, establishing an evaluation index system for nursing quality in patients with diabetes mellitus complicated by coronary heart disease. Results: The response rates for both rounds of expert correspondence were 100.00%. The expert authority coefficients were 0.873 and 0.892, respectively, with Kendall’s coefficients of concordance being 0.231 and 0.318 (p < 0.05). The final nursing quality evaluation system comprised 3 primary indicators, 11 secondary indicators, and 32 tertiary indicators. Among the primary indicators, process quality had the highest weight (0.467), followed by structural quality (0.284) and outcome quality (0.249). Within the secondary indicators, blood glucose management and cardiovascular risk management had relatively high weights. Conclusion: The constructed evaluation index system for nursing quality in patients with diabetes mellitus complicated by coronary heart disease demonstrates good scientific validity and systematicness, providing a reference basis for evaluating and continuously improving nursing quality in these patients.