For integrated light source cannot be easily realized with small emitting angle, a method of designing narrow beam for high-power COB light source is proposed. According to light distribution of the source and the desired light distribution of emergent rays, an optical system with Refraction-refraction(R-R) was chosen. The source model was established based on spectral distribution and relative intensity of the chosen COB light source, and then the divergence angle of a Lambertian source was reduced to 60° by using the Compound Parabolic Concentrator(CPC). Points on profile curves of the front surface and the behind surface of the lens were obtained with the extended conservation law and the Simultaneous Multiple Surface (SMS). Profile curves were obtained by curve fitting with these points, and then the lens model was established with three-dimensional software. The optical system was simulated with ray-tracing software. The results show that the divergence angle of the system is controlled within 30° in the optical port, the angle of the half of light intensity is 11.336°, and the total luminous efficiency is up to 89.398%.