A novel coupling system,taper duct applied to planar laser diode array(LDA) was proposed.The radiation angle of emergent beam is compressed by using the refraction principle.The transmission principle of taper duct was described on the basis of a ray-tracing method,and the good transmission characteristic was gained by using computer simulations.The results show that a nearly Gaussian distribution can be obtained in near-field when incontinuous light beams in space from LDA pass through the taper duct,and the taper duct,which has the simple structure and high efficiency,balances the beam quality in fast-slow axis direction.Moreover,the radiation angle and facula dimension of emergent beam are both quite small.