Abstract: Objective To analyze the correlation between optimal catheter placement length of peripherally inserted central catheter(PICC) and body weight of preterm infants. Methods The clinical data of 150 preterm infants who underwent PICC catheterization in the neonatal intensive care unit of the hospital from May 2018 to May 2019 were retrospectively analyzed. The position of catheter tip was measured by chest radiography and the optimal placement length of PICC catheter on chest radiograph was obtained within 24 h of catheterization, and the weight data on the day of catheterization was obtained. The PICC catheterization and catheter vein distribution were described. Pearson correlation analysis and unitary linear regression analysis were used to explore the correlation between optimal placement length of different catheterization veins and body weight. Results Of the 150 preterm infants, there were 89 cases(59.33%) with PICC catheter tip reaching the optimal position, 28 cases(18.67%) with catheter placed too deep, 12 cases(8.00%) with catheter placed too shallow and 21 cases(14.00%) with abnormal catheter pathway. The arrival rate of optimal position of basilic vein was the highest(66.22%), and the incidence rate of deep placement of basilic vein was also the highest(22.97%), and the incidence rate of shallow placement of great saphenous vein was the highest(20.00%), and the incidence rate of abnormal pathway of cephalic vein was the highest(32.00%). Pearson correlation analysis showed that there was a positive correlation between optimal placement length and body weight of different PICC catheterization veins in preterm infants(all P<0.05). Unitary linear regression analysis showed that there was a linear relationship between the optimal placement length and body weight of different PICC catheterization veins in preterm infants(all P<0.05). Conclusion The incidence rate of PICC catheter ectopy is higher in preterm infants, and there are some differences in the distribution of ectopic conditions in different catheterization veins. Clinically, the appropriate catheterization veins should be selected in combination with the specific circumstance of preterm infants. The optimal placement length of PICC catheter in preterm infants has a certain correlation with body weight and can be used to guide PICC catheterization, but the specific regression equation is subject to further clinical validation.