The invention relates to optical resonators, in particular to a high-quality-factor whispering gallery mode microspherical cavity preparation method. The method includes steps: 1) fixing a millimeter-scale quartz glass rod to a rotating motor; 2) adopting a CO2 laser for ablating the top end of the millimeter-scale quartz glass rod to a required microspherical cavity size to obtain a micron-sized quartz glass rod; 3) using the CO2 laser for ablating excessive length at the top end of the micron-sized quartz glass rod, and heating the micron-sized quartz glass rod to obtain an original whispering gallery mode micro cavity; 4) increasing output power of the CO2 laser, and firing the original whispering gallery mode micro cavity in a short time to enable the heated micro cavity to form a spherical shape naturally under the action of surface tension, so that a high-quality-factor whispering gallery mode microspherical cavity is obtained. By adoption of the method, on-column microspherical cavities can be obtained, and high stability is achieved. The method is applicable to preparation of microspherical cavities being 190-700micron in size and being 108 or above in quality factor.