In this paper, a sensor capable of simultaneously measuring refractive index of two kinds of media is proposed. The sensor consists of a single-layer graphene, a thin dielectric layer, a dielectric cavity A and a multilayer photonic crystal with a defect layer (i.e. a dielectric cavity B). When the incident light is introduced from the graphene side, the terahertz Tamm plasmon-polaritons (TPPs) mode at the interface between graphene and thin dielectric layer and the defect mode in photonic crystal are simultaneously excited. These two modes interact and couple to form an asymmetric Fano resonance absorption spectrum. The absorption peak wavelength coincides with the excitation wavelength of TPPs mode and is exclusively sensitive to the refractive index of the medium in cavity A, while the absorption Valley wavelength matches the defective mode wavelength and is solely sensitive to the refractive index of the medium in the defective layer. Therefore, the simultaneous detection of the refractive index of the two media can be realized. Numerical simulation results demonstrate that the sensor achieves refractive index measurement ranges of 1.3~1.46 and 1~1.005 for media in cavities A and B, respectively, with corresponding sensitivities of 0.125 THz/RIU and 0.6 THz/RIU. The study in this paper provides novel approach for simultaneous multi-medium refractive index measurement by leveraging coupling between TPPs modes and distinct modes.