We obtain a bottle beam by focusing a Bessel beam with the semiconductor laser as the light source to realize the tunability of a bottle beam. The plano-convex cylindrical lens and the gradient index lens are used for beam shaping to obtain a laser beam with a variable divergence angle, and thus a size tunable bottle beam is obtained. The numerical simulation results show that, when the divergence angle of the beam incident on the axial cone varies continuously in the range of 0°-1.5°, the maximum radial size of the bottle beam can be tunable in the range of 90.23-64.05 μm, however the length of the bottle beam varies from 1.85 mm to 1.47 mm. A tunable bottle beam makes optical tweezers more flexible.