Bound states in the continuum (BICs) can significantly enhance spin-selective light-matter interactions. However, current BIC metasurfaces generally rely on single or multiple chiral BIC modes to enhance circular dichroism (CD), which limits their application in functional integrated devices. This paper proposes a method that utilizes the strong coupling effect in BIC metasurfaces to achieve intrinsic CD with both high quality factor (Q-factor) and high efficiency. The metasurface is designed with a silicon-based cross-shaped nanohole array, which can simultaneously support a TM-like BIC mode and a TE-like guided-mode resonance (GMR) mode. By introducing under-etching to break the out-of-plane symmetry and tuning in-plane asymmetry parameter, strong coupling between the quasi-BIC (QBIC) mode and the GMR mode can be induced, thereby realizing near-perfect intrinsic CD with high Q-factor. In the strong-coupling region, the resonant wavelengths of the QBIC and GMR modes exhibit an anti-crossing behavior, while their imaginary parts of the eigenfrequency cross; the corresponding Rabi splitting energy reaches a minimum of 3.16 meV, and the induced intrinsic CD achieves a maximum of 0.995 at the wavelength of 1653.9 nm with a high Q-factor of 1083. Evolution of far-field polarization singularities shows that under strong coupling, the Γ point corresponds to a left-handed circular polarization singularity (C-point). Furthermore, the strong-coupling-induced CD exhibits good robustness—even under considerable variations in structural parameters, the high-Q and high-efficiency CD response is maintained. This method offers a novel design strategy for integrated chiral photonic devices and holds promise for applications in areas such as chiral sensing, chiral lasers, and nonlinear chiral optics.