Skin ulcers are one of the complications of diabetes. At present, the treatment of diabetic skin wounds is still not satisfactory, and the efficiency of drug delivery is limited by the depth of penetration. Herein, a synergistically flexible microneedle dressing is presented for effectively promoting diabetic wound healing. Metformin, as an anti-diabetic drug, can be loaded into microneedles, which can effectively pierce into the skin of diabetic rats to trigger a response for regulating blood glucose levels. A novel multifunctional nanosystem CaO2@polydopamine (CaO2@PDA) was introduced into polycaprolactone and gelatin (PCL/Gel) electrospun nanofiber films as microneedle back patches to inhibit inflammation, provide oxygen, and absorb the excess exudate. Besides, the CaO2@PDA in back patches also provided effective antibacterial properties against both S. aureus and E. coli. Additionally, the as-fabricated flexible microneedle dressings loaded with metformin and CaO2@PDA nanoparticles demonstrated a high level of CD31 and low level of TNF-α, leading to accelerated diabetic skin-wound closure. These distinctive features demonstrate that our microneedle system can be a facile candidate for efficient wound healing in patients with diabetes and may be applied in various biomedical fields.