In recent years, bound states in the continuum (BIC) in optical metasurfaces have garnered significant attention owing to their unique properties. Because of the interaction of two accidental quasi-bound states in the continuum (A-QBIC) modes, we explore the related novel optical phenomena in an all-dielectric metasurface that comprises a square nano-aperture array. It is shown that the A-BIC phenomenon can occur under x- and y-polarized normal incidences but exhibits the interaction of the two A-QBIC modes under 45° polarized incidence. The A-QBIC modes, which are analyzed using band and multipole expansion theories, are primarily governed by the toroidal dipole. Notably, the high Q-factor of the A-QBIC modes not only allows for the implementation of highly sensitive refractive index sensing but also facilitates the realization of flexible tunability of the interaction between the two A-QBIC modes, thereby achieving an analogue of electromagnetically induced transparency and tunable slow-light. Our results provide a feasible strategy to develop a high Q-factor meta-device based on A-QBIC in highly sensitive refractive index sensing and slow-light applications.