LED light source can be collimated by total internal reflection (TIR) structure which is widely used in LED secondary optic system design. By adjusting the total reflection surface of TIR structure, the circular illumination with small divergence angle is realized. The lenses with 5° and 10° half divergence angle are designed and the simulation experiments are performed. Simulation results show that the expectation requirements can be met and half divergence angle is 5° and 10° respectively with a point source or a 1 mm×1 mm LED source. This method can also be applied to design the lens with small divergence angle.