The Chinese Academy of Engineering Physics Terahertz Free Electron Laser Facility (CAEP THz FEL, CTFEL) is the only high-average power free electron laser terahertz source based on superconducting accelerators in China, with the advantages of continuously adjustable frequency (0.1-4.2 THz), high peak power (＞0.5 MW), high average power (＞10 W), high repetition rate (54.17 MHz), short pulse (～ps), narrow bandwidth (～2%), full coherence and linear polarization. Since the first lasing in 2017, it has been running stably for more than four years, and many experimental studies have been carried out. To further meet the demands of users, an upgrade plan for an infrared terahertz free electron laser facility based on CTFEL is proposed, where the electron beam energy is increased to a maximum of 50 MeV, and the spectrum range is expanded to 0.1-125 THz. Meanwhile, two experimental stations for material spectroscopy and biomedicine will be built.