Abstract: Objective The setup method based on planned bed value was proposed to improve setup accuracy under Orfit plate and body surface fixation of intensity-modulated radiation therapy （IMRT） patients of breast-conserving surgery. Methods A total of 29 cases of IMRT patients after breast-conserving surgery were selected and all patients were fixed with body surface fixation and Orfit in the supine position. The same patient was setup according to the skin markers （conventional group） and the planned bed value （experimental group） respectively. All patients after cone-beam computed tomography （CBCT） scan were matched with the CT images by rigid registration and the setup errors in three directions lateral（Lat）, longitudinal （Lng）, and vertical （Vrt） were obtained. Meanwhile, the body mass index （BMI） value and the maximum breast thickness value before treatment were collected for correlation Pearson analysis with the difference of all directions. Results The setup errors in the lateral direction, longitudinal direction, and vertical direction of the conventional group were （-0.01±0.32） cm, （-0.03± 0.23） cm, and （-0.20±0.38） cm respectively. The setup errors of the experimental group were （-0.04±0.31） cm, （0.04±0.22） cm, and （-0.06±0.23） cm successively. The setup errors in the Lng direction and Vrt direction between the two groups were statistically significant （P<0.05）. There was no statistical significance in the Lat direction （P>0.05）. BMI value was correlated with the setup errors of the conventional group （Vrt direction r=-0.435, P=0.018） but not correlated with the setup errors of the experimental group （P>0.05）. Breast thickness was not correlated with the directional pendulum errors in both groups （P>0.05）. Conclusions The setup accuracy of the planned bed value was better than skin markers, which indicated that it might have potential clinical benefits for breast cancer patients with radiotherapy under Orfit plate body surface fixation.