The invention discloses a metasurface-based cassegrain antenna, and mainly aims to solve the problems that the existing cassegrain antenna is high in phase error, complex in structure, and long in focal length. The metasurface-based cassegrain antenna comprises a carrier (1), a main reflecting mirror (2), an auxiliary reflecting mirror (3), a feed source (4) and a supporting structure (5); the carrier adopts a convex structure; the main reflecting mirror is conformal with the carrier; each of the main reflecting mirror and the auxiliary reflecting mirror adopts a phase change metasurface structure established based on generalized Snell law, wherein the auxiliary reflecting mirror is located below the focal point of the main reflecting mirror and has a hyperbolic characteristic phase, and is used for dispersing the electromagnetic waves emitted by the feed source into spherical waves; the main reflecting mirror and the auxiliary reflecting mirror are connected through the supporting structure; and the virtual focal point of the auxiliary reflecting mirror coincides with the focal point of the main reflecting mirror, and the solid focal point coincides with the phase center of the feed source. By virtue of the metasurface-based cassegrain antenna, the focal length of the cassegrain antenna can be shortened, wave beam calibration can be realized; and meanwhile, the antenna phase compensation error is lowered, the structure is simple, and the antenna can be used for communication and radar.