Abstract: We propose a metasurface with tunable circular dichroism extrinsic chiral based on the phase change material Ge₂Sb₂Te₅ (GST). The metasurface is composed of two symmetrical square silver split ring resonators and a GST intermediate layer arranged periodically. Combined with the oblique incident light, this metasurface is capable of achieving electromagnetic properties similar to that of the chiral structure. Numerical simulation results show that in the frequency range of 50 THz~300 THz, the maximum circular dichroism (CD) of the metasurface is 0.85 in the amorphous state of GST and 0.52 in the crystalline state of GST. When the GST switches between two states (amorphous-crystalline), a tunable frequency of about 70 THz is achieved. Compared with the reported works, the CD of this metasurface is larger and the tuning range is wider. By studying the electric field distribution, the origin of the circular dichroism is explained; and the effects of incidence angles and structural parameters on the CD of this metasurface are investigated. This research will have potential applications in efficient polarization modulation devices, circular polarizers, and polarization filters in the optical frequency band.