New generation on-chip sensing system puts forward the requirements of miniaturization, integration, low cost, etc. Silicon-based integrated waveguide devices adapt to its development trend, and the sub-wavelength grating structure is favored in the field of refractive index sensing because of its unique mode distribution characteristics. In this paper, first, the operating principles of the sub-wavelength grating waveguide are introduced, focusing on its advantages in the field of refractive index sensing. Then, the latest research progress of refractive index sensing based on subwavelength grating structures are sorted out according to the classification of device structures, and their advantages and disadvantages are analyzed and summarized simultaneously. Finally, the future development of refractive index sensing based on sub-wavelength grating structures is discussed.