A cylindrical micro-cavity is made by immersing a silica optical fiber into a low refractive index dye solution.Optically pumped by evanescent wave along the fiber axis,a long dye gain distance along the fibre axis is obtained,and lasing emission supported by Whispering-Gallery-mode in cylindrical micro-cavity is observed.When a fibre diameter 288 μm is immersed into three glass capillaries filled separately with Rhodamine 6G,Rhodamine 610 and Rhodamine 640 dye ethylene glycol solution,Whispering Gallery Mode laser oscillation in the wavelength ranges of 567~575 nm、605~614 nm and 656~666 nm are observed,three-color lasing emission (red,orange and yellow) from a single optical fibre is realized.The obtained lasing spectra are mode assigned,the spatial intensity distributions of the assigned modes and pumping energy along the fiber′s cross section are calculated.The computational results show that dye gain is confined in the evanescent field of Whispering Gallery Mode of the fiber,which leads to a high pumping efficiency and a long gain distance along the fiber axis.