A spiral-shaped plastic optical fiber (POF) surface plasmon resonance (SPR) refractive index sensor based on wavelength modulation was studied. First, the plastic optical fiber was prepared into a spiral by mechanical hot pressing and deforming method, and then a metal film with a certain thickness (about 50 nm) was deposited on the spiral-shaped POF by magnetron sputtering to stimulate the SPR effect, thereby forming a spiral-shaped POF-SPR sensor. By modifying the structure of the spiral-shaped POF-SPR sensor, the effects of different structural parameters on the refractive index sensing properties were studied. The experimental results show that the spiral-shaped POF-SPR sensor deforming from a flat POF with a thickness of 500 μm and a thread number of 4 has the better linearity and refractive index sensing characteristics, and the measured sensitivity in the refractive index range of 1.335~1.400 is 1 262 nm/RIU. The proposed sensor has the advantages of low cost, simple preparation and stable structure.