Objective To compare the clinical effects of midline’s tip at different position. Methods From September 2020 to January 2021,a multi-center randomized controlled study was used to select 384 inpatients as the research subjects from 6 tertiary A general hospitals in Zhejiang province,Fujian province,Jiangsu province,and Liaoning province. They were randomly divided into 3 groups according to random numbers generated by Excel. The midline’s tips were located in the subclavian vein in the experimental group 1,in the axillary vein of the chest in the experimental group 2,and at the distal of the axillary vein in the control group. The incidences of catheter-related complications（including phlebitis,catheter-related thrombosis,catheter-related infections,catheter occlusion,catheter dislodgment,bleeding,oozing） were compared in 3 groups,as well as unplanned removal rate due to complications,catheter indwelling time,and the incidence of abnormal intima after midline removal. Results A total of 384 patients were included. The total incidence of catheter-related complications in experimental group 1,experimental group 2,and control group were 9.93%,14.63%,and 34.17%. Unplanned removal rate due to complications were 2.13%,4.07%,and 13.33% in 3 groups. Catheter indwelling time were 12.00（8.00,19.75） d,12.00（8.00,21.00） d,and 10.00（6.00,17.75） d. After the removal,the incidence of abnormal intima were 0.75%,1.69%,and 6.36%. The differences of 3 groups were statistically significant（P<0.05）. Among them,the differences in the total incidence of catheter-related complications and unplanned removal rate between the experimental group 1 and the control group,the experimental group 2 and the control group were statistically significant（P<0.017）;the difference between the experimental group 1 and the experimental group 2 was not statistically significant（P>0.017）. In terms of the catheter indwelling time,the difference was statistically significant between the experimental group 1 and the control group（P<0.017）. Conclusion When the tip of midline catheter is located in the axillary vein of the chest or subclavian vein,the incidence of catheter-related complications is lower,with longer indwelling time and better clinical outcome.