Abstract: In order to adjust the size of bottle beam which was not adjustable flexibly in a current optical system, a novel optical system composed of one frustum and one axicon with different conical angle was proposed. The beam transformation property of this new system was analyzed by diffraction integral and Hankel wave theory. When a plane wave passes through the novel optical system, a bottle beam is formed and the size of bottle beam can be adjusted by changing the relative position between both the optical elements. Based on the analysis, the relevant parameters of bottle beam were also calculated by geometrical optics. The intensity distribution of bottle beam in different positions after the novel optical system was simulated by TRACEPRO software and the intensity distribution with the change of the relative position between frustum and axicon was also analyzed. The result of simulation is consistent with the result of theoretical analysis. The conclusion shows that bottle beam with adjustable size can be generated by the novel optical system.