All-dielectric metasurfaces based on bound states in the continuum (BIC) are widely used in the field of micro-nano biosensors due to their ultra-high quality factor (Q), which can effectively enhance the interaction between light and matter. In this paper, a rectangular all-dielectric dimer metasurface based on BIC is proposed. The finite element method is used for simulation, and time-domain coupled mode theory is employed for theoretical analysis. For the parameters of the two rectangular components in the metasurface, such as their angles, refractive indices, widths, and heights, four different symmetry-breaking modes are designed. All of these modes realize the transformation from symmetry-protected BIC (SP-BIC) to quasi-BIC (QBIC), with the maximum Q factor reaching 1.75 × 10⁴. These four breaking methods cover the current common SP-BIC breaking methods and provide choice for designing devices. After introducing the same asymmetric parameters, the QBIC resonance excited by the metasurface under the four control modes is dominated by magnetic dipoles. The sensitivity of the designed sensor device is almost at the same level, while the difference in figure of merit (FOM) can reach three orders of magnitude. In addition, under the same control mode, the sensitivity and FOM of the metasurface with positive breaking are higher than those with negative breaking when the absolute values of the breaking parameters are equal. After optimization and adjustment, the sensitivity and FOM of the metasurface reach 395 nm/RIU and 3502 RIU^–1, respectively, and its comprehensive performance index is better than those in most of existing studies. The metasurface provides an effective means for sensing detection in the biological and medical fields. At the same time, this research offers a new insight into the design of refractive index sensors based on BIC.