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), limiting 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 a high quality factor (Q-factor) and high efficiency. The metasurface is designed as 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 the in-plane asymmetry parameter, strong coupling between the quasi-BIC (QBIC) mode and the GMR mode can be induced, thereby achieving near-perfect intrinsic CD with a high Q-factor. In the strong-coupling region, the resonant wavelengths of the QBIC and GMR modes exhibit anti-crossing behavior, while the 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 a wavelength of 1653.9 nm, with a high Q-factor of 1083. The 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.