Background: To explore the optimal irradiation technique for breast cancer after mastectomy and immediate breast reconstruction. Methods: Ten breast cancer patients undergoing immediate breast reconstruction after mastectomy were included. We compared the target volume coverage, doses to breast implant and organs at risks (OARs) using seven techniques, including three-dimensional conformal radiation therapy (3DCRT), field-in-field intensity-modulated radiation therapy (FIF-IMRT), the mixture of 3DCRT and IMRT (HYBRID), IMRT, flattening filter-free (FFF)-IMRT, volumetric-modulated arc therapy (VMAT) and FFF-VMAT. Results: IMRT, FFF-IMRT, VMAT, and FFF-VMAT had better conformity index compared to 3DCRT, FIF-IMRT, and HYBRID. The IMRT and FFF-IMRT had the improved homogeneity index in comparison with VMAT and FFF-VMAT. IMRT and FFF-IMRT also had significantly lower dose to breast implant compared to 3DCRT, FIF-IMRT, and HYBRID. However, the volume of ipsilateral lung receiving 10 Gy (V10) and mean dose of ipsilateral lung in VMAT and FFF-VMAT were higher than those of other techniques. The dose to ipsilateral lung in IMRT was in the range of traditional radiation techniques and VMAT. The V10 of heart in IMRT, FFF-IMRT, VMAT, and FFF-VMAT were significantly higher than that of other techniques, and the V40 were improved in IMRT, VMAT and FFF-VMAT compared with 3DCRT, FIF-IMRT, and HYBRID. The FFF technique did not affect the dose to target volume coverage, breast implants, and OARs in IMRT and VMAT. Conclusions: Among the seven radiation techniques, IMRT achieves similar or superior target volume coverage and a better breast implant sparing.