The application of 4th radial order whispering-gallery mode (WGM) on refractometric sensor is investigated. A microcapillary resonator with 4.8 μm wall thickness is researched in experiment and the sensitivity difference among different modes is observed. The highest sensitivity of 48.74 nm/RIU (refractive index unit) and detection limit of 6.2×10-6 RIU are achieved. The 4th order WGM resonant spectrum can be picked out clearly by comparing with the simulation results, and it shows a significant advantage against other modes in sensor sensitivity. In addition, the temperature dependent resonant wavelength shifts of different orders WGM are calculated. The 4th order WGM shows a lower response to temperature fluctuations comparing with other low radial modes. This may provide a solid theoretical and experimental foundaiton to build practical refractometric sensors with high sensitivity and low noise.