Objective To compare the effectiveness and safety of three PICC catheterization methods guided by intracavitary electrocardiogram (IC-ECG) combined with ultrasound in critically ill patients, and to provide a reference for clinical PICC catheterization practices. Methods A total of 188 critically ill patients receiving PICC between December 2023 and August 2024 were divided into three groups according to the catheterization time:modified sheath delivery (MSD, n=63), one-needle tunneled (ONT, n=60), and two-needle tunneled (TNT, n=65). Results Significant differences were found in first-attempt puncture success, catheterization success, procedure time,incidence of bleeding and catheter dislodgement rate among the three groups (all P＜0.05).Specifi-cally, MSD and TNT had higher success rate of first-attempt puncture and catheterization than ONT, and MSF was faster than both ONT and TNT (both P＜0.017). Bleeding was highest in TNT, while catheter dislodgement was highest in MSF (both P＜0.017). Conclusion The modified sheathdelivery PICC technique features high efficiency and a low incidence of bleeding, but bears a high risk of catheter dislodgement.The one-needle tunneling PICC has a low dislodgement rate but lower first-attempt success and longer procedure time; the two-needle approach has high first-attempt success but higher bleeding and more complex operation.The optimal method should be chosen based on individual patient factors.