Purpose: To investigate the causes and the nursing interventions of vasovagal syncope (VVS) during ultrasound-guided Modified Seldinger Technique (MST) PICC catheterization. Methods: Clinical data (medical records, demographic data, diagnosis, local vascular compression situation, B-mode ultrasound-recorded catheter/vessel ratio and the occurrence time, symptoms and treatment of syncope) of 14 patients diagnosed as vasovagal syncope during ultrasound-guided PICC catheterization at three hospitals in Guangdong province from September 2018 to September 2019 were collected for this retrospective analysis. Results: There were 3091 cases of ultrasound-guided MST PICC catheterization in the venous catheter outpatient clinics of the 3 hospitals from September 2018 to October 2019 with 14 cases (0.45%) of intraoperative vasovagal syncope, all cancer patients (5 males, 9 females) with a mean age 45± 3.8. They all received PICC for the first time and were under mental stress during the operation. Among the 14 patients (2 mild, 7 moderate, 5 severe), 8 had multiple lymphadenectasis in the neck and clavicular areas of the catheterization side, which resulted in different degree of venous compression and difficulty in insertion; 5 had catheter/vessel ratio over 45%. 2 cases of VVS occurred when the patients were asked to turn their heads against shoulders on to the puncture side; 10 occurred when using B-mode ultrasound probe to examine the jugular vein; 2 occurred when pulling out the catheter sheath. Conclusion: The related factors of vasovagal syncope during ultrasound-guided PICC catheterization include overcompression and avulsion on blood vessels and mental stress. Therefore, it is recommended to implement psychological interventions before surgery, reduce compression and avulsion of the vascular access during catheterization, and improve practitioners’ abilities in vessel selection (vessels with a catheter/vessel ratio less than 45%) and catheterization skills to eliminate the incidence of vasovagal syncope during PICC catheterization.