To address the critical challenges faced by core online banking systems in the financial industry during post−quantum cryptographic migration—including business continuity risks, poor compatibility across massive terminal devices, and high−concurrency performance bottlenecks—this paper proposes and implements a full−stack quantum−resistant cryptographic migration architecture for large commercial banks. The architecture adopts a dual−signature fusion mechanism that combines a hybrid TLS (transport layer security) secure channel with the Chinese national cryptographic standard SM2 and the ML−DSA (module−lattice−based digital signature algorithm). This design establishes an end−to−end evolutionary path spanning from underlying hardware terminals to network transmission and further to backend cluster signature verification. Gray−scale high−fidelity validation conducted in a real online banking environment of a commercial bank demonstrates that, under a concurrent transaction pressure of 1000 TPS (transactions per second), the hybrid secure channel establishment response time is optimized to 3.5 ms, and the single signature verification latency is approximately 13.6 ms. This empirical study preliminarily validates the feasibility of high−dimensional lattice−based cryptographic algorithms under the test environment and workload described herein, providing a replicable engineering demonstration for the smooth post−quantum evolution of critical information infrastructure in China's banking sector.