Background <p>China is adopting and promoting the mini-midline catheter insertion technique, which requires professional training to ensure its application and patient safety. This study aims to explore the effectiveness of the Train-the-Trainer model in nurse training for Mini-Midline Catheter Insertion.</p> Methods <p>A medical center selected venous therapy specialist nurses for mini-midline catheter procedure training, after which these nurses became trainers and guided other nurses. The research utilized a mixed-methods design, incorporating puncture condition surveys and open-ended questions. Over the following six months, outcomes such as catheter insertion success rates were monitored, and nurses’ interviews were analyzed using the Kawakita Jiro method.</p> Results <p>A total of 675 mini-midline catheters were inserted in the study, with a success rate of 97.54%. The success rate for first-attempt punctures was 86.51%, with 584 successful cases and no catheterization-related complications. After training, expert consultations for catheter issues decreased from 28.46 to 9.25%. Additionally, three key themes of the training were identified: (1) enhancing nurses’ professional sense of achievement and job satisfaction through skill mastery; (2) familiar groups and environments are more conducive to improving training effectiveness; and (3) the multifaceted role opens up a brand new path for the professional development of nurses.</p> Conclusion <p>The mini-midline catheter insertion training program based on the “train-the-trainer” model effectively ensures the standardization of nurses’ techniques and the safety of punctures while also cultivating educators and thus deserves widespread promotion.</p> Clinical trial number <p>Not applicable.</p>