The Wireless Local Area Network (WLAN) has experienced tremendous changes through these days, both in usage and technological aspects. Recently, 802.11ac and 802.11ad protocols for WLAN have been standardized by IEEE. They are both amendments to the 802.11-2012 protocol and their primary Medium Access Control (MAC) technique is Distributed Coordination Function (DCF). What's more, in order to improve high speed throughput especially in MAC layer, 802.11ac and 802.11ad both extend frame aggregation mechanisms utilizing the MAC Protocol Service Unit Aggregation (A-MSDU) and MAC Protocol Data Unit Aggregation (A-MPDU) schemes and block acknowledgement (Block ACK) schemes. In this paper, we investigate the traditional analytical model of DCF. Then based on that model, we propose an adaptive Block ACK scheme to achieve higher throughput by reducing package loss. A MATLAB simulation is established to show that the proposed Block ACK enhancement can improve system performance.