This paper proposes the effective channel sounding algorithm for NDP sounding protocol in IEEE 802.11ac standard. The channel for wireless LANs changes slowly, and doesn’t need to feedback all the time. So we suggest the effective algorithm for NDP sounding with considering channel variation. To take channel variation into account, the algorithm uses mean squared error calculation, and compares with threshold to decide feedback or not. Finally, performance evaluation is carried out, and shows the reduction of total sounding time.