A new model of liquid axicon for producing a single bottle beam with tunable size is proposed. In the aspect of geometrical optics, it analyses the principle that how the liquid axicon produces the bottle beam is analysed, and meanwhile, the diffracting theory is used to simulate and demonstrate. It is concluded that liquid axicon can produce single bottle beam when the liquid refractive index of the injected liquid is higher than that of the axicon material. Through optics software TracePro the model of liquid axicon is established and the properties of the transmission conversion of the light beam are simulated. The influence upon the size, location of the bottle beam with different refractive index is calcalated and simulated, and the conclusion shows that, the lower the liquid refractive index is, the smaller the size of bottle beam is, and the theoretical analysis basically corresponds with the simulation result.