Objective To compare the dosimetric differences, plan complexity, verification pass rate, and execution efficiency of volumetric modulated arc therapy (VMAT) plans designed for post-mastectomy radiotherapy of breast cancer using Halcyon 2.0 and VitalBeam accelerators in flattening filter-free mode. Methods A retrospective analysis was conducted on imaging data from 87 female breast cancer patients aged 29 to 75 (49.9 ± 9.9) years who underwent modified radical mastectomy followed by radiotherapy. VMAT plans were designed using both VitalBeam and Halcyon accelerators in flattening filter-free mode. The dosimetric parameters, plan complexity, verification pass rate, and execution efficiency were compared between the plans designed for both accelerators, with a significance level of P<0.05. Results In terms of target volume parameters, Halcyon 2.0 plans demonstrated superior homogeneity index and conformity index. For organs at risk, the Halcyon 2.0 plans showed lower doses for the lungs (D_20% and D_mean) and heart (D_mean) compared to the VitalBeam plans (all P<0.05). Regarding plan complexity, Halcyon 2.0 plans exhibited better median average aperture area variation (0.35 ± 0.02), smaller aperture score, and larger median plan aperture area than VitalBeam plans (all P<0.05). However, VitalBeam plans had a superior median modulation complexity score (0.28 ± 0.01) compared to Halcyon 2.0 plans (P<0.05). Patient plans were assessed using the ArcCHECK phantom, revealing higher pass rates and significantly shorter execution time for Halcyon plans compared to VitalBeam plans (P<0.05). Conclusion Both Halcyon 2.0 and VitalBeam accelerators can provide high-quality VMAT plans for postoperative radiotherapy of breast cancer, with excellent verification pass rates ensuring treatment accuracy and efficacy. However, Halcyon 2.0 offers lower plan complexity, simplifies the treatment planning process, and reduces execution time, thereby achieving higher treatment efficiency and demonstrating greater advantages in clinical applications.