A comprehensive study on the whispering gallery mode (WGM) lasing characteristics of a rhodamine 6G (R6G)-based flexible bottle-like microcavity has been performed. The closed-loop WGMs excited inside the microcavity were found strongly confined along the radial direction. Thus, the spacing of ultralow loss lasing modes can be realized by controlling the diameter of the bottle-like microcavity. By studying the WGM lasing action, the dependence of lasing threshold and Q-factor on the radius of the microcavity was analyzed. The lasing threshold for the random gain medium was reduced under the influence of radial optical confinement by increasing diameter. In addition, the WGM lasing characteristics of the bottle-like microcavity were also explored by the three-dimensional finite-difference time-domain method. Our approach provides a solution scheme towards the research for lasing characteristic of novel nanocrystal fluorescence or quantum dot materials based on the flexible ultrahigh Q factor bottle-like microcavity.