A cylindrical microcavity was made by immersing a silica optical fiber in a dye solution. The pumping threshold energy of the whispering-gallery-mode (WGM) laser strongly related to the spatial overlapping between the evanescent field of the pumping laser and the WGMs, and it also was influenced by the losses of the WGMs of low and high order. The distribution of evanescent field of the WGM can be changed through changing the refractive index of dye solution and the diameter of fiber. Then the spatial overlapping and the losses of WGM are changed. The results show that there is a lowest pumping threshold value of the first order WGM laser when one of the refractive index of the solution and the diameter of fiber is changed but the other is invariable.