IEEE 802.11ah, which is also called WiFi HaLow, is considered to be a promising protocol for Internet of Things (IoT). The legacy 802.11ah proposes a number of grouping mechanisms, which are based on the hierarchical organization, to relieve channel access’s collision in the IoT’s communication environment. However, the legacy 802.11ah still cannot effectively avoid collisions in a crowded environment. This work proposed the Registration-based Collision Avoidance (RCA) mechanism to avoid collisions and furthermore reduce the waiting time of backoff. The RCA mechanism lets the AP know the network situation in advance and then schedule stations to avoid collision. Comparing with the legacy 802.11ah, experimental results shown that the proposed RCA mechanism has the lower collision rate and better throughput when the number of stations in a time slot is high.