Beam Position Monitors (BPMs) are essential in parti-cle accelerators for the precise measurement of beam trajectories. Considering the inherent inaccuracies in manufacturing and assembly, rigorous offline calibration processes are essential to guarantee the precision of beam position measurements. The predominant calibration technique, specifically the wire test method, is tailored for relativistic beams and is inappropriate for low-β beams. This manuscript introduces an innovative ap-proach employing a helical slow-wave structure to emu-late the electromagnetic fields of low-energy beams, thus facilitating the calibration of BPMs for low-β scenarios. Employing a helix-based calibration platform, we con-ducted the calibration of the nonlinear response of BPMs at the Xi'an Proton Application Facility for a 7 MeV pro-ton beam, with results aligning with the simulation. This advancement expands the precision and range of beam position measurements, substantially enhancing the op-eration and optimization of particle accelerators.