In this study, we study the pulley type ring resonator with the gold ring to produce surface plasmon resonance by waveguide coupling. Since the generation of the surface plasmon is particularly sensitive to the change in the refractive index, the device can be served as a biomedical sensor. The finite-difference time-domain method (FDTD) is used to solve the Maxwell’s equations to evaluate the performance of the device. The electromagnetic field distribution (EMF) inside and outside the ring resonator can be calculated by the FDTD method. By changing the ring radius, we investigate the device sensitivity. In this work, the sensitivity can be as high as 602.6nm / RIU.