Purpose <p>The Beijing Electron–Positron Collider (BEPC) is a circular accelerator operating in the τ-charm energy region, which has been operational since 1988. The facility comprises a linear accelerator (Linac), two transport lines, and two collider rings. Originally, the Linac operated at an energy of 1.3&#xa0;GeV at BEPC; this was increased to 1.89&#xa0;GeV at BEPCII. To meet evolving physics requirements, a recent upgrade has further raised the Linac energy to 2.35&#xa0;GeV, with the capability of accelerating beams up to 2.8&#xa0;GeV.</p> Methods <p>The microwave system is essential for the stable operation of the Linac. It comprises four subsystems: the microwave excitation system, the radio frequency (RF) distribution system, the sub-harmonic buncher system, and the low-level RF system. Designed to support long-term, stable operation for electron–positron collision experiments, the system also meets the technical requirements for wakefield acceleration verification experiments. Beam energy requirements are fulfilled by incorporating a pulse compressor and two klystrons—referred as an energy enhancement. Additional operational demands are addressed by improving system stability and replacing equipment with degraded performance. The former involves upgrades to the microwave excitation and low-level RF systems, while the latter includes the replacement of sub-harmonic bunchers and pulse compressors.</p> Results <p>The outcomes of the energy enhancement and system upgrade are in accordance with the expected requirements.</p> Conclusion <p>The upgraded microwave system is capable of meeting the latest operational requirements and maintaining long-term stable operation.</p>