The coupling system consisting of microcylinders and lens duct is an important part of high power all-solid-state lasers. Its coupling performance has direct influence on the laser′s output power and beam quality. The rays distribution inside the system and on the lasering crystal surface should be studied to optimize the coupling system′s structural parameters. Utilizing a 3D ray-tracing method, the real spatial lights propagating through mocrocylinders and lens duct are traced and the energy transfer efficiency and light distribution are calculated. The coupling characteristics of a hexahedral lens duct and a tapered lens duct are compared. The results show that the hexahedral lens duct needs a bigger length and can achieve higher energy coupling efficiency, while the tapered lens duct can get the light distribution closer to round and the length can be very short.