Objective To explore the guiding effect of Intracardiac Electrocardiogram specific Q wave on catheter tip localization du-ring the implantation of upper arm infusion port. Methods A total of 124 patients undergoing Intracardiac Electrocardiogram assisted upper arm infusion port implantation were divided into an intervention group (non-purely high-tip P wave）with 63 cases and a control group （purely high-tip P wave） with 61 cases according to the P wave shape in electrocardiography.In the intervention group, specific Q wave localization method was used to determine the length of catheter insertion.In the control group, the length of catheter was determined according to the group standard of the Intracardiac Electrocardiogram method for positioning the tip of peripherally inserted central catheter released by the Chinese Nursing Association.X-ray examination was performed to compare the accuracy of catheter tip location between the two groups.At the same time, the difference between the actual length of the catheter and the length of the catheter determined by using the body surface measurement, the P/R wave amplitude 50% localization, and the double peak P wave localization respectively in the intervention group. Results The accuracy percentage of catheter tip location in cavoatrial junction and lower 1/3 segment of superior vena cava were 98.41% and 100% respectively in the intervention group and the control group, there was no significant difference between the two groups （P＞0.05）.In the intervention group, the length of the catheters determined by body surface measurement and 50% P/R wave amplitude localization were significantly shorter than the actual length of catheters （both P＜0.05）, while there was no significant difference when the length of the catheters determined by using the double peak P wave localization （P＞0.05）. Conclusion The specific Q wave localization method is more accurate and applicable for the patients with non-purely high-tip P wave, so it can be used as a supplement of Intracardiac Electrocar-diogram localization technology.