A model of helical groove structure is proposed. The surface plasmons excited by the incident light with different spin angular momentum have different intensity distributions on the structure, attributed to the coupling of the helical groove structure and the optical spin angular momentum. So the spin angular momentum of incident light can be obtained by the intensity distribution of surface plasmons excited by the helical groove structure. The finite element method is used to calculate the extinction ratio of the surface plasmon excited by the left-handed polarized light and the right-handed polarized light at the center of the spiral groove. The maximum extinction ratio reaches 168, which can distinguish the photons with different spin angular momentum. In the numerical simulation, the intensity extinction ratio for different incident wavelengths is analyzed. The extinction ratio of the incident light wavelength in the range of 600~740 nm is above 50, with a best extinction ratio in the wavelength of 670 nm. In addition, the effect of the helical groove structure parameters on the extinction ratio is illustrated. And the maximum extinction ratio is obtained with the groove width of 200 nm, the groove depth of 70 nm, and the turn number of 2, at this time, the spiral groove structure has the best ability to detect the optical spin angular momentum. This work could provide a new approach to detect the optical spin angular momentum in integrated optics.