To investigate the applicability of fiber Bragg grating(FBG) sensing techno logy for the testing of vortex-induced vibrations of deep-sea risers, this paper describes laboratory tests of vortex-induced vibrations(VIV) of a model deep-sea riser in a stepped current. The experiment was carried out in a large-scale wave and current coupling tank, and FBG sensors were used for data acquisition. Model materials were made of copper. The riser, 6.2 m long with a slenderness ratio of 310, was tested in conditions in which the upper 1.2 m was exposed to a uniform current, while the lower 5.0 m was in still water. 48 grating measuring points were symmetrically equipped along the riser. According to changing the external flow velocity, internal flow velocity, and initial top tension, the vibration performance of the riser such as vibration frequency, amplitude and mode under different working conditions were observed, and the VIV rule of the riser was analyzed in a stepped current based on strain data and modal theory. The results indicate that the requirement for FBG technology to test the VIV of deep-sea risers with a large slenderness ratio can be satisfied. The vibration performance such as strain history, amplitude and vibration frequency was accurately demonstrated. Multi modal characteristics of the riser under different external velocities were clearly reflected, and the lock in region was seen clearly under each dominant frequency.