Unstable drone landing scenarios have caused severe damage to expensive drone-based devices. It is required to provide precision altitude information of the drone during its landing maneuvers. In this paper, we propose a device-free wireless localization algorithm, by adopting channel state information (CSI) to assist drone landing. By adopting our proposed system, the drone will not need to carry any additional sensing devices for precise positioning. The commodity Wi-Fi access points only need to be installed near the landing nest of the drone, which means that multiple drones can use the same set of landing systems. Experimental results show that our proposed system can provide centimeter localization precision for drone landing applications. With the device-free feature, system resources can be effectively utilized and costs are greatly reduced.