Based on slot waveguide structures, a polymer-based microring operating at around 890 nm wavelength was proposed and designed. A detailed analysis of modal characteristics of the slot waveguides were carried out from refractive index sensing. The relationships between the sensitivity and the waveguide height, width and slot width were analyzed. Conventional bend slot waveguide had a large propagation loss, which had a bad influence on the quality factor Q and the extinction ration of the microring. An asymmetric slot waveguide was designed which could make the mode propagate in the middle of the waveguide and then decrease the bending loss. A strip-slot mode converter based on multimode interference (MMI) structure was designed for better coupling between strip and slot waveguides. Simulations show that the sensitivity of the designed microring resonator could reach 109 nm/RIU.