To address the problems of complex joint configurations and low construction efficiency in traditional precast wall panels connected by grouted sleeves, a novel precast wall panel structural system with a composite keyway–sleeve connection is proposed. In this system, the keyway provides interface shear resistance and positioning functions, while the sleeve-connected reinforcement primarily resists tensile forces, forming a coordinated load-transfer mechanism that integrates both shear and tensile resistance. Based on full-scale experimental specimens, a refined finite element model was established using ABAQUS, and a cohesive–friction hybrid interface model was introduced to simulate the mechanical behavior of the joints. The accuracy of the model in predicting failure modes and load–displacement responses was verified. Parametric finite element analyses were conducted to systematically investigate the effects of axial compression ratio, height-to-width ratio, and connection strength on the lateral stiffness of wall panels. A simplified multivariate regression equation for the stiffness influence coefficient of precast wall panels was proposed. Taking a typical six-story precast residential shear wall structure as a prototype, a spatial analytical model considering connection stiffness reduction was established, and elastic analysis under frequent earthquakes as well as static nonlinear pushover analysis under rare earthquakes were carried out using MIDAS Building. The results indicate that the interstory drift ratios under frequent earthquakes satisfy the code requirements. Under rare earthquakes, the performance point on the capacity–demand spectrum is located in the stable post-yield stage, demonstrating sufficient seismic safety reserve. The middle and lower stories are identified as the primary regions of lateral deformation and strain concentration, and the structure exhibits significant directional stiffness differences. The research results demonstrate that the proposed keyway–sleeve connected precast wall panel system possesses the advantages of reliable connections, convenient construction, and clear load-transfer mechanisms, showing promising engineering application prospects and significant potential for practical promotion.