This paper analyzes and designs the structure of a sensor, the performance of which is evaluated by changing the refractive index. The structure of this sensor consists of two waveguides, eighteen cavities and nine rings. For better and more accurate results, we only change the refractive index of the middle ring and the refractive index of the other amplifiers remains constant. The results show that with increasing and changing the refractive index, the resonance wavelength will shift. This means that this method can be used to understand the refractive index and resonance wavelength. By changing the wavelength and refractive index and calculating the resonance amplitude curve (FWHM), three characteristics of sensitivity coefficient, figure of merit (FOM) and quality factor Q can be examined. These three characteristics, especially the sensitivity coefficient, tell us whether this sensor has a good performance or notIn this structure, the sensor sensitivity has reached 6591 nm / RIU. This means that the performance of the proposed sensor is better and more powerful than similar sensors and can achieve a more flexible amplitude of the wavelength. Also, the maximum figure of merit (FOM) is 43.73 nm / RIU and the highest quality factor Q is equal to 60.01. In the end, we come to the conclusion that this method has tremendous potential for use in various fields of measurement, such as biochemical, medical and military analysis. Also, all the diagrams obtained in this research have been drawn using MATLAB program.