This trial evaluated the effects of insulin aspart (IAsp) and insulin detemir and metformin on islet function in newly diagnosed type 2 diabetes mellitus (T2DM). A total of 96 T2DM patients were randomised into the control group (insulin detemir + metformin treatment) and the study group (insulin detemir + metformin + IAsp treatment), with 48 cases each. The study compared clinical outcomes, as well as changes in fasting plasma glucose (FPG), 2-hour postprandial blood glucose (PBG), glycated haemoglobin (HbA1c), fasting insulin (FINS), homeostasis model assessment of insulin resistance (HOMA-IR), HOMA-beta, quality of life, and sleep quality scores before and after treatment. Compared to the control group, the study group showed a higher total effective treatment rate, lower levels of FPG, 2-hour PBG, HbA1c, FINS, HOMA-IR, and sleep quality scores, while demonstrating higher HOMA-beta and quality of life scores (all p < 0.05). Insulin detemir + metformin + IAsp was effective in treating T2DM, significantly enhancing insulin function and blood glucose levels, quality of life, and sleep quality. This combination therapy, though not commonly utilised in newly diagnosed T2DM patients, offers a novel therapeutic approach in clinical practice.