The present invention relates to a graphene-dielectric composite metasurface-based reflection type broadband polarization controller, and belongs to the technical field of novel artificial electromagnetic materials and terahertz science. The polarization controller comprises a four-layer structure, wherein the lowermost layer is a metal substrate (1), the middle is a low-refractive-index dielectric (2), and the uppermost layer is a high-refractive-index dielectric metasurface array (3) embedded in the low-refractive-index dielectric (2); and meanwhile, the upper surface of the metasurface array is exposed in air, and uniform single-layer graphene (4) is arranged between the low-refractive-index dielectric layer and the high-refractive-index dielectric metasurface. A bias voltage control device (5) is arranged between the graphene layer (4) and the metal substrate (1), so that linearly polarized light is converted into orthogonal linearly polarized light or circularly polarized light ina certain frequency range by changing the conductivity of graphene. The reflection type broadband polarization controller integrates the dual functions of a half-wave plate and a quarter-wave plate,and has the advantages of high efficiency, simple structure, easy integration and the like.