Abstract: Objective: To investigate the impact of uncorrected setup errors of helical tomotherapy for the different parts of tumors. Methods:A total of74patients were treated with helical tomotherapy, among which there were 20head and neck tumors, 17thoracic tumors, 22upper abdominal tumors and 15pelvic tumors. All patients received MVCT scan prior to treatment delivery. A combined total of 1757 scans were analyzed. The range of the scanning fractions was be-tween 10and 33. The average value was 24. Results: For different parts of tumors, the corrected error rate for the Z-axis was the smallest, with a ratio for <3mm of 82.35%-95.99%. For the X-axis, the ratio for <3mm was 51.45%-74.67%. The er-ror rate for the Y-axis was the largest, with a ratio for <3mm of 68.3% for head and neck tumor. The ratios of corrected error for the other parts were 41.81%,42.47% and 31.90%, respectively. The ratio for the Y-axis for >5mm on pelvic tumors was 47.96% , and the others on thoracic and abdominal tumors were 34.89% and 30.69% . The ratio for >5mm on head and neck tumors was only10.64% .Conclusion: With helical tomotherapy technique, the corrected error could be used as a guide to greatly improve the precision of the treatment area by allowing the technician to correctly design the planning tar-get volume (PTV) and then modify the plan accordingly during treatment.