Objective To investigate the mini-midline catheter insertion methods to improve the success rate of first-attempt puncture and reduce complications.Methods A total of 130 patients who were going to undergo surgery to place mini-midline catheters were randomly divided into the control group and the observation group, with 65 cases in each group.In the control group, catheters were inserted into the superficial forearm vein without the help of any tools.In the observation group, ultrasound-guided placement of mini-midline catheters was performed, and the catheters were placed in the upper arm vein.We observed and compared the success rate of first-attempt puncture, how long it took to place the catheters, the complication rate, and the catheter dwell time between the two groups.Results Sixty-four cases in the control group and 63 cases in the observation group completed the study.The success rate of first-attempt puncture in the observation group （96.83%) was significantly higher than that of the control group （85.94%）.The lower incidence of phlebitis were found in the observation group, with significant differences.The time for catheterization and catheter dwell time in the observation group were significantly longer than that of the control group （all P＜0.05）.Conclusion The ultrasound-guided placement of mini-midline catheters can improve the success rate of first-attempt puncture, reduce the incidence of phlebitis, and prolong the catheter dwell time.