Carrier sense multiple access/collision avoidance (CSMA/CA) in wireless local area network (WLAN) is considered as a complex protocol for modeling due to its autonomous function and influence of interference with medium shared by multiple nodes. IEEE 802.11ax, a sixth generation WLAN standard, enables various flows with different modulation coding scheme (MCS) and traffic load, transmission power (TxP), clear channel assessment threshold (CCAT) to coexist in a WLAN. This variation makes modeling of WLAN system more difficult. This paper proposes a throughput model for high efficiency WLAN analysis under any traffic load and MCS condition. This model factorizes throughput into five elements. This flexible model can be applied to any complex topology. In simulation evaluation, a correlation coefficient between the results of the proposed model and simulation is observed by at most 0.981. Furthermore, The results shows that the influence on the throughput due to the change in TxP is correctly modeled and minimum TxP for maximum throughput is revealed on a condition.