Abstract: A metamaterial terahertz sensor based on tri-resonant absorption peak was designed, and the unit structure was composed of a metal super surface, a polyimide (PI) medium layer and metal base plate. The metal super surface contains two symmetrical multi-open rings and two metal short rods in the center of the inner ring. The performance of the sensor was simulated using the time domain finite integral method, and the results show that the sensor has three narrowband resonant absorption peaks at f₁=0.498 2 THz, f₂=0.713 8 THz and f₃=0.960 2 THz, and the absorption rates are 93.92%、99.95% and 99.91%, respectively. When the surface of the sensor is covered with analyte, the sensitivities of the three resonance absorption peaks are 71.5, 121 and 190.3 GHz/RIU respectively, and the frequency shift and the average value of the frequency shift of each resonant peak are linear with the refractive index of the analyte.