IEEE 802.11ac standard provides an increase in performance by introducing the pioneering downlink multi-user MIMO technique which allows simultaneous transmission to multiple clients in the down-link direction [1]. In this paper we have evaluated MU-TXOP sharing probabilities in IEEE 802.11ac at different traffic intensities using analytical model based on discrete Markov chain and E-limited M/G/1 queuing model. Our results show that the low priority traffic group benefits most from MU-TXOP sharing and achieves 150% throughput gain at low traffic (12 Mbps).