Objective To evaluate the effectiveness of different external length of PICC in cancer patients. Methods Totally, 340 cancer patients were randomly assigned to control (n=168) and experimental (n=172) groups. The external length of PICC was 7 cm in the control group and 5 cm in the experimental group. The incidence of catheter-related adverse events were compared between the two groups. Results The incidence of dressings that don′t completely cover the insertion site, dressing lifting, catheter dislodgement, and unplanned dressing change were significantly lower in the experimental group compared with the control group (all P<0.05). Conclusion The external length of PICC of 5 cm is better for PICC securement and reduces the occurrence of catheter-related adverse events.