A double-layered cylindrical microcavity is fabricated by filling Rh6G dye solution into a fused capillary. By pumping with s- and p- polarized laser light respectively, whispering-gallery mode lasing emission with transverse magnetic and transverse electric polarization is observed. The interference modulation effect in the whispering-gallery-mode lasing spectra is found when pumped by s- polarized light. And the modulation period increases with the refractive index of dye solution, but decreases with the ratio of the external to internal diameter of a capillary. By applying the interference modulation theory on the reflective and refractive waves in the double-layered cylindrical microcavity, the observed phenomenon can be explained successfully. The interference modulation effect provides a certain reference for mode selection in a multimode whispering-gallery-mode laser.