Abstract: A transmitting antenna with tapered fiber is proposed to transform the divergence partially coherent light formed by multi-mode fiber to collimate light. This structure can produce a partially coherent light of low divergence and guarantee the output power of laser transfers completely. It is applicable to laser communication in atmosphere. Based on the ray tracing method, the divergence angle of random rays which incidents on the small section of tapered fiber in tapered fiber is analyzed. The propagation property of all the rays incidents on the small section and the angle of incidence less than numerical aperture angle are investigated. The result shows that the emission angle of these rays could be improved to less than the half of the taper angle in theory, if the length of the tapere