Abstract—LTE Licensed-Assisted Access (LAA) to unlicensed spectrum has been considered as an effective complement in offloading growing traffic since its emergence at 3GPP. Since 2015, 3GPP has launched standardization to develop LAA as a key technology for LTE-Advanced unlicensed spectrum deployment in Rel-13. In this paper, an analytical model is built for the performance evaluation of typical coexistence of Licensed-Assisted Access (LAA) LTE and WiFi IEEE 802.11. Assuming that LAA eNode-B performs Channel Clear Assessment (CCA) in a manner similar to Carrier Sense Multiple Access (CSMA) of WiFi, we use a two dimensional Markov chain to help analyzing not only the affected performance of WiFi but also the relation between the joint system performance and LAA maximum transmission time. After analytical analysis and simulations, it is shown that under certain system configuration joint system performance is approximately inversely proportional to a monomial of the maximum LAA transmission time.