Abstract: Since wireless channels have the characteristics of short-term reciprocity and space-time uniqueness, key extraction based on wireless channel state information (CSI) can establish shared key between legitimate communication parties. This technique is considered to be an effective complement to the upper layer encryption scheme with the advantages of low computational complexity and no need of additional facilities. In this paper, we designed a CSI-based key extraction scheme for legitimate wireless communication nodes, and a passive eavesdropping scheme for eavesdropping nodes. Furthermore, we implemented the prototype system of proposed schemes under the time division duplex orthogonal frequency division multiplexing communication system. Finally, we conducted key extraction test experiments in the presence of eavesdropping nodes under two typical communication environments (indoor and outdoor), in each of which we considered both static and mobile nodes. Analysis of test results verify the short-term reciprocity and space-time uniqueness of the wireless channel, and show that the proposed key extraction scheme can achieve considerable key performance and strong system security in typical communication scenarios.