In this paper, a terahertz metamaterial sensor based on double opening ring is proposed, which can be used to detect the refractive index and thickness of materials. The structure of the sensor consists of two parts: a metamaterial structure with two open square rings and a ring nested inside, and a polyimide substrate. When the terahertz wave is perpendicular to the surface of the metamaterial, three high-Q resonance peaks are formed in the range of 0.8 ~ 1.8 THz. By discussing the relationship between the surface current distribution and the formation of three resonance peaks, it is observed that the different response characteristics of the metamaterial structure to the incident terahertz wave lead to different surface current distribution. In addition, the applications of the sensor in refractive index sensing and thickness sensing are also explored. The sensing sensitivities of 170 GHz/RIU, 103 GHz/RIU and 119 GHz/RIU for the resonant frequencies f1, f2 and f3, respectively, at a given thickness, all of which have superior sensing characteristics and can be used for high-sensitivity refractive index sensing with their multiple resonant peaks. This highly sensitive refractive index sensor can detect small changes in the analyte to be measured and has promising applications in the field of biochemical detection.