We propose a novel annular focus antenna with an off-axial parabolic primary mirror and slanting hyperbolic secondary mirror. Ray tracing based on three-dimensional vector reflection theory is utilized to design and analyze the structural parameters of the antenna. In ideal conditions, there is no geometric loss in theory and the transmitting efficiency increases by 24.54% compared with the conventional Cassegrain optical antenna. The transmitting efficiency is also calculated in the conditions of off-axial and on-axial defocus. The simulated results demonstrate that this design can increase transmission efficiency of the optical antenna effectively.