This work presents a single-layer Z-shaped chiral metasurface based on quasi-bound states in the continuum(Q-BICs) . The proposed structure simultaneously achieves an ultra-high quality factor and strong circular dichroism(CD) , thereby overcoming the intigh-Q resonance and chiral response in conventional chiral metasurfaces. Unlike traditional multilayer or three-dimensional chiral structures that require complicated fabrication processes, the proposed metasurface adopts a planar monolayer configuration with broken in-plane mirror symmetry, offering offering improved fabrication compatibility and scalability. By introducing an in-plane asymmetry parameter into the Z-shaped air-hole unit cell, the symmetry-protected BIC mode was transformed into a chiral Q-BIC mode, resulting in a high CD value of 0.95 with an extremely narrow linewidth of 1.98 nm. Furthermore, dynamic tuning of the chiral response was achieved through oblique incidence by adjusting the elevation and azimuth angles of the incident wave, which enabled the excitation of extrinsic chirality without changing the metasurface geometryof the structure. The study further analyzed the physical origin of the strong chiral resonance through multipole decomposition and electromagnetic field distributions. The results reveal that the intrinsic chiral response induced by in-plane symmetry breaking is dominated by the magnetic quadrupole(MQ) , whereas the extrinsic chiral response under oblique incidence mainly originates from the toroidal dipole(TD) . In both cases, the resonance quality factor followed an inverse-square dependence on the corresponding asymmetry parameter, consistent with the inverse-square scaling law of Q-BIC systems. Benefiting from the narrow resonance linewidth and strong localized electromagnetic field enhancement, the proposed metasurface was further employed as a near-infrared refractive index chiral sensor. The sensor achieved a high sensitivity of 252 nm/RIU, an high figure of merit of 2471.03 RIU^-1, and a quality factor of 15089 while maintaining strong CD characteristics. Compared with previously reported chiral sensing platforms, the proposed structure exhibits superior overall sensing performance and better fabrication tolerance. These findings not only provide a feasible strategy for realizing high-Q and high-CD chiral metasurfaces using a simple monolayer architecture, but also offer valuable insights for applications in nonlinear optics, integrated photonic devices, polarization manipulation, and ultrasensitive biochemical sensing.