We demonstrate a novel silicon-on-insulator dual-microring resonator for sensing application. Numerical analysis shows that the Q factor of dual-microring resonator is three orders of magnitude higher than that of conventional single-ring resonator with lossless waveguide and thereby as a sensor, the resolution and minimum level of detection is enhanced greatly. For the resonance peak of inner ring, a Q value of 1.07 × 107 is achieved theoretically in weak coupling conditions while the sensing area is kept below 50 × 50 μm2. Detection limit of refractive index change of 3.85 × 10-6 can be achieved for bulk refractive index sensing. Moreover, by enlarging bending radius of the outer ring, Q factor can be further improved. The analytical description of output spectrum response is derived. In addition, for low propagation loss waveguide, critical coupling condition of two rings and bus waveguides is obtained and it's essential for sensor device optimization.