Abstract: Objective To compare the dosimetric difference between prone position and supine position in breast cancer radiotherapy after breast-conserving surgery. Methods Strict inclusion and exclusion criteria were drew up. Trials were searched from PubMed, FMJS, CHKD and WanFang full-text database. Studies of the dosimetric comparisons between prone position and supine position in radiotherapy on organs at risk after breast-conserving surgery were included. Standardized mean difference and 95% confidence interval were computed by statistical software RevMan5.2 provided by the Cochrane collaboration. Results Finally, 16 trials containing 442 patients were included. The results of Meta-analysis showed that the radiation exposure of ipsilateral lung (SMD=-4.36, 95% CI: -5.41－-3.31, P<0.001) and the heart (SMD=-0.24, 95%CI: -0.4－-0.09, P<0.05) were dramatically lower in prone position than those in supine position, while the doses to contralateral breast did not differ between the two positions (SMD=0.19, 95%CI: -0.02~0.40, P>0.05). Conclusion Compared with supine position, prone position in breast radiotherapy is contributed to a significantly lower radiation dose for ipsilateral lung and heart of patients after breast-conserving surgery.