Abstract: Objective To investigate the physical parameters of helical tomotherapy for abdominal tumor and errors occurred in image-guided MVCT treatment. Methods Twenty patients with abdominal tumor received helical tomotherapy. Setting parameters including field width（2.5cm）, pitch（0.3mm） and modulation factor（2.5mm） were selected. Before treatment,all patients underwent MVCT scanning. MVCT images were registered with automatic KVCT plan and used to readjust the registration according to the dose distribution. The setup errors were obtained and analyzed. Results The minimum and maximum values for the errors on x,y,z directions were（1.205±0.207） mm and（6.496±2.165） mm,（2.600±0.671） mm and（2.600±0.671） mm,（0.880±0.18） mm and（5.151±1.821） mm,respectively. Conclusion MVCT can improve the accuracy and precision of tumor treatment and may help to design the PTV for abdominal tumor.