IEEE is making an 802.11ax protocol for next-generation wireless network. The goal of 802.11ax is to improve the networking performance of individual device, especially those mobile stations with numerous access networks in high-density wireless network. However, traditional 802.11 standards have the problem of poor transmission efficiency because traditional standards for wireless network enhance the overall wireless network volume and are easy to be implemented. When there are numerous wireless networking devices existing in a congested network to continuously conduct random access procedure, the success rate of channel access might drastically drop, leading to problems such as data error, loss, latency, energy consumption, etc.; to improve this problem, when designing message processing mechanism in physical layers, we should also consider the problem of media access control. Hence, this paper proposes a collision detection and avoidance media access mechanism for next-generation WiFi communications. The proposed algorithm leverages the ability of underlying random access to compatible legacy WiFi and identifies available slot-time to avoid channel collision of the access network. The algorithm's performance is evaluated by the simulation which demonstrates significant improvement in terms of channel efficiency as well as transmission delay. The results confirm that the proposed CSMA/CDA scheme provides a better performance than the legacy CSMA/CA in dense WiFi networks.