The preparation of surface-enhanced Raman scattering (SERS) substrate with both structural stability and SERS activity under extreme pH conditions faces several problems, including tedious preparation, time consuming processes, high cost, and the need for professional equipment and personnel. Herein, a facile preparation protocol for a large-scale nanoarray film substrate was developed for multi-purpose SERS sensing. Through a simple self-assembly process under specific conditions, well-ordered, highly sensitive, structurally tunable, acid-alkali resistant and disposable “polyamide@Ag” coralloid nanoarrays were fabricated. Due to the dense distribution of AgNPs on the top and side surfaces of the nanoarrays and optimized geometric construction, a large number of controllable Raman “hotspots” formed in the space, resulting in excellent Raman signal uniformity and SERS performance for Rhodamine 6G. To evaluate the potential application of this flexible substrate, it was implemented in the label-free trace determination of folic acid with a limit of detection as low as 5.24 × 10⁻¹² M. Importantly, the as-prepared polyamide@Ag nanoarrays exhibited high structural stability over a wide pH range from 1.25 to 12.00, which is beneficial for the detection of non-pH-neutral samples. The results demonstrated that this hybrid substrate has broad application prospects in fields as diverse as biosensing and environmental monitoring.