Wireless local area network (WLAN) technology can be seen everywhere in people’s lives, and technology itself is constantly developing, the coming new WLAN standard IEEE 802.11ax is excepted to increase the per-user throughput by 4 times than existing WLAN standards in residential, enterprise and other dense deployment scenarios. One of the key technologies of 802.11ax is spatial reuse (SR) technology, which improves area throughput by allowing concurrent links, and spatial reuse parameter (SRP)-based SR mechanism is introduced in 802.11ax. But in fact, the SRP mechanism lacks the ability to adapt to the scenario, and does not guarantee full gain from SR in any dense deployment, even exhibit a negative gain in some scenarios. This paper proposes a probability based SR (PSR) mechanism to achieve the full gain from SR with a probability value that reflects the scenario condition. Simulation results indicate that the PSR mechanism is a practical solution for SR in next generation WLAN (NGW).