We propose a split mirror ring terahertz metamaterial sensor with the material of gold and quartz, based on the bright-bright mode coupling of the plasma-induced transparency, that significantly improves the Q-factor of the two bright modes, and the Q-factor of the resulting transparent window is as high as 13.15. The generation principle of each resonance peak was analyzed through the electric-magnetic diagram. The theoretical refractive index sensitivities of the transparency and the two resonance valleys were obtained by simulation with 410, 490, and 480 GHz/RIU, respectively. Moreover, after normalization, we compared the theoretical refractive index sensitivities with similar sensors and found that the sensor we proposed performs better. Therefore, the excellent sensing performance makes the sensor promising for markerless and nondestructive testing.